Why wouldn’t you just make a singular card that punishes all colors evenly
Like...
At the start of game declare a color your commander is that color in addition to its original colors
Your commander deals damage to you equal to each devotion in the mana cost of a spell that includes the declared color, all damage is considered commander damage
Make a card that reads...
At the beginning of a new game declare a color. Your commander is that color in addition to its other colors and types
Your commander gains,”for each devotion of the chosen color in a spells mana cost, your commander deals 1 damage to you”.
Your can only get so much commander damage correct
Like...
At the start of game declare a color your commander is that color in addition to its original colors
Your commander deals damage to you equal to each devotion in the mana cost of a spell that includes the declared color, all damage is considered commander damage