Hello Steffen,

Yes its possible to do so with astah* professional or astah* UML.

1. Go to the property of the project and check the language you want to model with in the [Project Setting] tab














2. Create a Class "Color"
3. Go to the property of the Class and check <<enum>> in the [Language] tab (In the sample figures, we have selected Java)









4. Create an attribute "red", and go to the attribute's property and select <<enum constant>> from its [Language] tab








5. Create an attribute "blue" and do the same as above
6. Create an attribute "green" and do the same









Hope it helps.

If you don't have an astah* professional or astah* UML, free evaluation license is available! Read the [Evaluate] in the page below.
http://astah.change-vision.com/en/shopping/steps.html

Cheers,
Satomi