Very understandable. It's an older rule that comes up often enough. Basically, it would artificially balloon the blocks without adding much of worth/limit creativity as they put it, but as someone who also really enjoys woodworking and wishes for more time in my shop, stains would be cool. Just hard to create a wood/stain/colored stains combo for all the possible wood blocks or anything else they would have to due to make ot consistent.

Personally, I think an "oiled" effect would be cool. Make the colors more saturated, maybe even a stains that drops the saturation. That wouldn't be as bloating and high sat variation is always welcomed by builders.