This is something that happens with some built-in perl variables and also when using regexes sometimes. With the built-in variables I use () around them to make the syntax colouring work out, like this

I didn't test in this particular case, but that should work better. using "" may alter behaviour (or not), so I'm less keen on using that...

Highlighting with regexes can be more cumbersome to correct, but that's not the problem you have right now ;)

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ecocode