Yes this is possible by using your color field as the basis of the value list, so in the Edit Value List dialog you need to select the option to 'Use values from field:' and then specify the table your Color field is on and select it.
I hope this helps.
I can't seem to get this to work. It allows me to enter any value but I lose the drop box and other values.
Is your dropdown on a PORTAL? If so, I had a similar problem and found that all fields on the portal row had to be completed and that I needed to put a "on Exit" scripttrigger on the last field that did a "Record Commit". When I did this, FM updated the dropdown list with the last entered value. (Yes I know. This is weird behavaior but it seems to be BUG IN FM 10 ADV)
I could get the same result by clicking outside the portal and clicking back in it again.
Hope this helps.
Are you still having trouble with this, or is it working now?