New answers tagged silicone
You could try sanding it with 1000 or 1500 very fine grit. The paint will then probably 'take hold'
Paint over it (or to either side) and ignore the strip where the paint won't stick. Pull it out and re-caulk with something paintable. Try to smear paintable silicone over the top of it and hope that sticks to the stuff you have. Hard to do neatly, pulling it out and redoing is more likely to succeed, IMHO.
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