overloading operations for enums

[Dominikus Dittes Scherkl via Digitalmars-d-learn]

Hello.

I want to create some finite algebra, where the elements are 
enumerated but operations on them are defined (with composition 
tables).

e.g.:

enum color = { white, yellow, red, blue, orange, violet, green, 
black };

color a = blue;
a += yellow;
assert(a == green);

is this possible in D?

Because, if I define a struct, I can define operation overloads, 
but then I have no enumeration of possible values. But if I 
enumerate, I cannot
overload operations.
What have I missed?