The chromeColor style will not do what you need. The purpose of the chromeColor is to easily apply a tint to UIComponents. You are applying a white tint to a grey color, which results in grey. You will have to create your own skin to achieve something more.
Is there a reason you don't want to create a custom skin? It will give you much more control over the look / feel of your button.
Another option would be to create a custom component that extends spark.components.Button and adds a style that you could use to change the exact color of your button. This would give you what you are looking for, but be much more work than creating a skin.
Hope that helps.
Thank you for replying to my old unanswered question!
The reason why I tried to avoid creating a new skin is because it's quite some work (yet another file to be added to one of my packages), just for changing a button's color...
Note that I was relatively new to Flex when I wrote this topic. About 4 years ago!
However, in the meanwhile, I figured out that's just the way Spark components seem to work, and if I don't like their look, I must create a new skin.
It would be so much easier if you could just change a property like "backgroundColor" and maybe set another property "chromeEffect" to false, but anyway, Flex != HTML/CSS, and I think what Adobe calls CSS in Flex is far from being something close to CSS as defined by the W3C... :-)
Thanks again for your attention and information.