Add a toggle to change the color from black to white

[AliceChurchfield]

I use the floor bar when configuring Stiletto settings. It can be a bit hard to see it when the character's shoes are black. If I could just toggle it at will between black and white, that would basically solve the problem.

[ManlyMarco]

I suggest making a PR, it seems like a good beginner project. Look for new Color in https://github.com/ManlyMarco/Illusion_HeightBar/blob/master/Shared/HeightBar.cs