simple predicate

[bill1001]

Im trying to figure out how write a predicate which replaces any occurence of a known color in a list with the word 'choice'. Known colors: red, green blue.
Eg:

?-color([the,hall,is,red,the,room,is,blue,and,green],R).

R=[the,hall,is,choice,the,room,is,choice,and,choice]
More(y/n)

Any help would be greatly appreciated.
Thank you.

 

[chipperMDW]

Here's a start. Try to fill in the rest yourself.

is_color( red ).
is_color( green ).
is_color( blue ).

color( [], [] ).

% Replace the head of the list with 'choice'
% if it's a color
color( [ H | T1 ], [ choice | T2 ] :-
    ????,
    ????.

% Otherwise, leave that element alone
color( [ H | T1 ], [ H | T2 ] ) :-
    ????.

Hint: it's a recursive predicate.

Extra: How can you rewrite "is_color" so you can specify colors like this??

valid_colors( [ red, yellow, blue ] ).
valid_colors( [ orange, green, purple ] ).