White caulk is the first color most DIY boaters reach for when resealing a hatch or fitting aboard their boat. After all, white matches most boats. But consider that white caulks begin to look grey as grit and sand become impregnated into the cured caulk over time. Additionally, many caulks mildew and look terrible because of it. Bottom line: White caulk often doesn’t blend in for very long.