Ensure alpha is a number in Color constructor

[lloydk]

Fixes two failing constructor tests.

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[jgerigmeyer]

Before, alpha could be passed in as NaN and it would be retained as such -- this now coerces it to 1. Is that intentional?

[lloydk]

Before, alpha could be passed in as NaN and it would be retained as such -- this now coerces it to 1. Is that intentional?

You're right, I think we need to allow NaN to be specified.

The getColor function checks alpha === undefined so maybe that's what we should do in the Color constructor.

color.js/src/getColor.js

Lines 27 to 29 in 44f3741

	if (color.alpha === undefined) {
	color.alpha = 1;
	}

Should getColor clamp alpha like the Color constructor?

[LeaVerou]

Oh good point. We do plan to eventually use null for none, rather than NaN, since that's a separate keyword, but for now we should coerce to NaN.

[lloydk]

I've added some additional constructor tests for NaN/none/clamping and alpha is set to 1 only if it's > 1 or undefined.