How Call $cat_yellow Using $cat . $color?

I have variables like:
$cat_yellow = "bob";
$cat_green = "doug";
$cat_brown = "dude";

and then let's say there is a POST variable like $color.

In PHP, I want to call one of the $cat_* variables. Let's assume $color = "green";

I try $favorite_cat = $cat . $color ;

Shouldn't that work? But that does not seem to work and I am not sure what to do. But, I think you can see what I am trying to do.

Any suggestions?
Thanks!

$favorite_cat = $cat . $color ;

This tries to concatenate whatever is in the variable "$cat" with what is in variable "$color". Wont work like you want.

You need to do:

$favorite_cat = ${'cat_' . $color} ;

ah, I see.

Thank you very much.