When a fiberglass part is laminated in a mold, the exterior colored gelcoat is applied first. If it is white gelcoat, then a dark colored gelcoat is them sprayed on over the white. When the lamination is done, this permits the laminators to see any dry spots or trapped bubbles in the fiberglass they are laying down and squeege them out.
This backup gelcoat is usually black, but if a colored sheer or bootstripe color is sprayed on, then it may be the backup. Tape is put on the mold in the area of the sheer and bootop stripe, the white is sprayed on for the hull color, the tape is pulled off, and then the the colored gelcoat sprayed on.
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