Make colour equality not approximate

[ElectroJr]

Currently the colour equality methods use MathHelper.CloseToPercent() instead of actually checking equality, which directly contradicts the method's own documentation. IMO equality should just check equality. If approximate equality is desired, that should be explicitly checked.

I'm not sure why exactly it was using approximate equality before. Maybe it was trying to avoid unnecessary shader/rendering changes? In which case maybe this PR should also update those checks.