The colour in polyurethane seals is irrelevant, it is just a dye, I worked is a urethane factory for 20 years, we used red, blue or green to suit the customer. Plain urethane can be white or toffee colour and either TDI, NDI, or MDI mix. It is the best all round material to use but sometimes too hard to easily seal in certain applications (high Shore hardness) which can be measured with a Durometer if you buy one.

Baz