Colorless unlocked, then steep difficulty spike

[Raoul589]

Up until colorless was unlocked, I found there was a reasonable pace of progress. Now I've hit a serious wall, because colorless seems to add very little in terms of value when first unlocked and yet the upgrades for colorless are very expensive to unlock any of its useful upgrades. I have 99% of the rest of the tree fully upgraded except for these expensive colorless upgrades.

It went very quickly from being fun to a horrible grind. What am I missing?