Color blending fixes

[jac8888]

The gradient code had the same rounding error in the color lerp that the border radius code did. I also fixed an error in the way the blending is done in the animation code. (More details here.)

[mikke89]

Thanks a lot! These are some great changes.

Could you perhaps move all the color interpolations into a separate function? They are quite verbose, and especially now that they are used several places.

[jac8888]

Sure thing; would you say that the lerp should be overloaded for Colourb to be like this?
Will add the clamp as well.

[mikke89]

Great. I think it's better to make a separate function for this one.

[jac8888]

I do think it makes sense to overload the lerp since it doesn't behave in the correct way for Colourbs (truncating rather than rounding the result leading to errors), and someone is likely to use the wrong function unknowingly if there is another one. I'm not really sure where else it would make sense to go (locally, another function in Math)?

[mikke89]

I figured it would be easier to separate them in case we later provide a way to select different color interpolation strategies. We don't really have a better place right now than math, that should be fine.

We could do a static assert to make sure people don't use lerp with Colourb.

[jac8888]

All right, I've made those changes. :)

[mikke89]

Awesome work! Thank you! :)