it might have something to do with ACETABLE.cpp, if you paste the code I can tell your for sure if it does, just the part relating to that expression. If it is the problem, you can probably figure out from this: the ADDEXP relating to the get color, check number 3 below, but here's a breakdown on the others as well, I don't remember if the tutorial went in detail:
[code:3scnhft6]ADDEXP("My expression", "My category", "MyExpression", &ExtObject::eMyExpression, RETURN_INTEGER);[/code:3scnhft6][/size:3scnhft6]
[*:3scnhft6]"My expression" should be what you see when in the Add Expression dialogue in the editor
[*:3scnhft6]"My category" is the category it's under
[*:3scnhft6]"MyExpression" is what you actually have to type to use the expression, like "Angle" is what is here in the sprite plugin's sprite.angle expression. not case-sensitive. Checking if this is an empty string is probably where I'd first look, or if it was invalid with a space or something that wouldn't work in construct.
[*:3scnhft6] &ExtObject::eMyExpression is a pointer to the c++ function that actually returns the value at runtime for this expression
[*:3scnhft6] RETURN_INTEGER is the return type of the c++ function. RETURN_STRING, or RETURN_FLOAT are two more valid constants, if you right-click - go to deceleration in visual studio on any one of these, you can see a full list.[/*:m:3scnhft6][/list:o:3scnhft6]
if it's not this, it's probably not to do with the ace_table, but I'd suggest checking number 3 before moving on to other troubleshooting