Long-time lurker here! I created a cube about 3-4 years ago, using some spare 150 dollar i had around. It was pretty much a crap-rare cube but it was a lot of fun to play with. The more i played with it, the more i wanted to expand, include new cards, etc. When i made the decision to take it more seriously, i had a look at other cubes and cards i was interested in playing. This eventually resulted in me deciding to go for a modern-only cube, ignoring the ban-list and making exceptions for commander-only-cards. My main reason for doing this is because i felt like some of the legacy cards (channel, power 9, etc) made the cube too.. unfair/swingy, etc. Combined with my love for multicolor cards, i came up with my current cube. It's by no means finished, and i'm buying upgrades for it every month, but i'm very happy with how things have progressed since the start.
One thing i've noticed, is that blue seems to struggle in the cube. Even with the recent addition of snapcaster mage, blue seems to remain a splash color. Now, this could be because of the people i play with just not liking blue, but i fear it might have something to do with my choice of going modern-only. Looking at other people's cubes, blue always seems to have the biggest amount of non-modern cards. The more power i add to the cube, the further blue seems to relatively fall behind.
I was wondering how others deal with power-disparity between colors? Do you accept it, do you purposefully weaken other colors or do you have other solutions?
Well, you're not wrong that the best blue cards are pre-modern. There's a reason blue dominates legacy/Vintage and is much less represented in Modern. It's not quite the same thing in cube, of course, because the specific cards that help blue in Legacy (most importantly Force of Will) aren't quite as important to the color in cube, but the fact is blue used to be super overpowered and other colors have had their time in the limelight since then.
That said, you have to remember that draft is a self-correcting format. If each color is even remotely playable (which is hard not to be the case in cube), then it will be played, but simply by fewer players, and it should help to even out the winrates. As such, it doesn't matter that much that colors aren't perfectly balanced. They certainly aren't in most powered (or unpowered but legacy) cubes, where blue is clearly the best color.
If they're too unbalanced for your tastes, here's a few ideas.
First, since you're still building your cube, you might want to concentrate on blue upgrades for a while. If you ever get to a point where you're satisfied with balance, you can then try to maintain it, which should be easier.
Second, perhaps the color has issues beyond just card quality. For instance, consider what kind of deck your blue cards go into, and whether you can cut some good cards that are "orphaned". Consider something like Chasm Skulker. It's a perfectly fine midrange or aggro card, but if the rest of your blue section is really geared towards hard control and combo, perhaps it doesn't fit.
Third, if your issue is that it isn't enough of a main colour, you could try to include cards that really reward for going really heavy on blue Cryptic Command is an obvious one you might already have, but Thassa, God of the Sea and Master of Waves are huge blue devotion rewards (though I should add that you should also support them with other heavy blue permanents, but you get the idea).
And finally, here's the big thing: your job as a cube designer is to make a fun draft environment. That's it. If you feel blue is missing something only available from older cards, you should feel free to add cards as you wish. Especially those cards that you feel would improve the color, but wouldn't really be weird in modern. Consider a card like Memory Lapse. It's obviously a strong piece of blue interaction, and while it's not legal in modern, similar cards exist there (Remand, Lapse of Certainty) so it wouldn't feel out of place.
Making a cube is kind of like dungeon mastering a game of DnD, if you've ever done that: rules are cool, but ultimately they're just a framework, and the real game is making a fun experience, which sometimes means cheating a little.
One thing i've noticed, is that blue seems to struggle in the cube. Even with the recent addition of snapcaster mage, blue seems to remain a splash color. Now, this could be because of the people i play with just not liking blue, but i fear it might have something to do with my choice of going modern-only. Looking at other people's cubes, blue always seems to have the biggest amount of non-modern cards. The more power i add to the cube, the further blue seems to relatively fall behind.
I was wondering how others deal with power-disparity between colors? Do you accept it, do you purposefully weaken other colors or do you have other solutions?
That said, you have to remember that draft is a self-correcting format. If each color is even remotely playable (which is hard not to be the case in cube), then it will be played, but simply by fewer players, and it should help to even out the winrates. As such, it doesn't matter that much that colors aren't perfectly balanced. They certainly aren't in most powered (or unpowered but legacy) cubes, where blue is clearly the best color.
If they're too unbalanced for your tastes, here's a few ideas.
First, since you're still building your cube, you might want to concentrate on blue upgrades for a while. If you ever get to a point where you're satisfied with balance, you can then try to maintain it, which should be easier.
Second, perhaps the color has issues beyond just card quality. For instance, consider what kind of deck your blue cards go into, and whether you can cut some good cards that are "orphaned". Consider something like Chasm Skulker. It's a perfectly fine midrange or aggro card, but if the rest of your blue section is really geared towards hard control and combo, perhaps it doesn't fit.
Third, if your issue is that it isn't enough of a main colour, you could try to include cards that really reward for going really heavy on blue Cryptic Command is an obvious one you might already have, but Thassa, God of the Sea and Master of Waves are huge blue devotion rewards (though I should add that you should also support them with other heavy blue permanents, but you get the idea).
And finally, here's the big thing: your job as a cube designer is to make a fun draft environment. That's it. If you feel blue is missing something only available from older cards, you should feel free to add cards as you wish. Especially those cards that you feel would improve the color, but wouldn't really be weird in modern. Consider a card like Memory Lapse. It's obviously a strong piece of blue interaction, and while it's not legal in modern, similar cards exist there (Remand, Lapse of Certainty) so it wouldn't feel out of place.
Making a cube is kind of like dungeon mastering a game of DnD, if you've ever done that: rules are cool, but ultimately they're just a framework, and the real game is making a fun experience, which sometimes means cheating a little.