You will have to color match since gelcoat naturally fades and oxidizes over time, making darker, more bold colors muted, and bright white colors can yellow or become an off white and lose their real finish. Start with a very small amount of yellow tint mixed in white gel coat. Keep dabbing it onto the original surface to get a comparison. It's a time consuming process even for a pro to match by eye. Yellow, brown and black should cover any of the typical boat interior colors. This article might be helpful: Color matching gelcoat – Jamestown Distributors
I just had to do this on my C309 and got a good color match with a tiniest bit of brown tint (patch in the cockpit area). yellow was far too yellow to help match. one area near the transom, ended up matching on basically pure white. so it definitely can vary from spot to spot based on fading and sun etc.