While updating the Gumbo-Components on this blog to flex 4 final I noticed that the style-property baseColor has been changed to chromeColor.
In addition to this the flag useChromeColor can be set to tell the SparkSkin to usechromeColor for colorization. For custom skins this can be set by overridinginitializationComplete() in the skin.
Internally Flex checks this flag in updateDisplayList() of a SparkSkin and uses the value in chromeColor for colorization (respecting exclusions in get colorizeExclusions()).
If you are using Gumbo-Components from this blog that use baseColor be sure to make these adjustments.
Also, the namespace was changed for halo from: