Anonymous Monk has given you two solutions to your problem, and yourself said you found out.

This is not exactly what you asked for, but I just want to add that whenever I feel like concatenating words to build a hash key I tend to separate them with a separator. For example:

$hash{'colour;red'} = 'RED';
$hash{'colour;blue'} = 'BLUE';
$t = 'colour';
print $hash{"$t;red"}
[download]

It is IMHO clearer to read and it can help preventing subtle bugs when two different pairs of words lead to the same concatenated result. Suppose you have the words "abc" and "defgh" and the words "abcd" and "efgh": they end up being concatenated into the same key. With a well-chosen separator, this cannot happen. Even a simple space can sometimes make a good separator. And it solves naturally the problem that you had (at least with some proper separators such as ";" ",", "|", "-", space, etc.).