You have an extra = before the props.fgcolor. Just as you don’t need it for the 'white' or 'black' results, you don’t need if for the props call either.
*The parentheses are not required but, in my opinion, help with readability.
**It’s probably just related to how you pasted the code into the post, but be careful - you have “smart” quotes around all the values, not run-of-the-mill, regular quotes.
There’s an initiative to bring expressions to chart widgets but it’s stale - I offered to extend the support of expressions to chart widgets so there’s no ambiguity which widgets accept expressions and which don’t:
As for the “that’s a pity” remark (and the “it’s a shame” I’ve read several times already wrt. the stuff I made for this community) I would have many things to say but I’ll restrain myself.