Well... I guess it wouldn't do any harm.. I may change that.
But TBH if you have code which isn't robust enough to deal with the callbacks and listeners being called in a different order, then something is probably wrong!
If the colour depends on the slider's value, then why keep a redundant copy of it that can be out-of-sync with the real value?
Unless calculating that colour is incredibly slow and the result needs to be cached for performance, then it'd be a much better design to simply have a const method that calculates and returns the colour based on the slider's value, and to never actually store it anywhere. Less state is better!