fixed bug on 64bit ios

Using float instead of CGFloat resulted in a wrong color wheel, as hue, saturation and brightness always defaulted to 1.875. After some testing I found out, CGFloat is 4 bytes on 32bit and 8 bytes on 64bit.

See: https://developer.apple.com/library/ios/documentation/uikit/reference/UIColor_Class/Reference/Reference.html#//apple_ref/occ/instm/UIColor/getHue:saturation:brightness:alpha: