I know it's frustrating because the Template:Color is only working for limited templates, but I'm trying out a new one. The prototype I have is Template:PortableSTU48Infobox and is still in the works. For now, I've locked the color template so that it won't cause more despair. I'm also sorry for the less time I contribute...I had to retrieve several images for the NogiKoi Fandom, and I'm still only able to retrieve 10% of the current total images from the game.
It's not the first Portable Infobox I tried to produce. I also made Portable Infoboxes in NogiKoi Fandom and Majisuka Fandom. This is the third Fandom that I'll be trying to make one. I'll admit that changing the header background color will be the most challenging currently.