I bought the gelcoat match and patch kit and didn't find it worth the money. It come with 2 tiny tubes of uncoloured gelcoat and a bunch of tubes of different colours and a tiny tube of catalyst. My personal experience is that you are better off to buy a tub of unwaxed, raw colour gelcoat, and a bottle of white and a bottle of yellow pigment. Sometimes a brown can be useful but the raw product already has a brown colour naturally.
Watch Andy with boatworks today on his you tube channel, he has a 3 part video on colour matching gelcoat. It's not that hard if you go slow. You'll need lots of white, and a tiny drop of yellow. I also find my girlfriend's eyes are better at judging the colour.
You may want to mix in gelcoat wax or you can spray it with PVA (polyvinyl alcohol) after it starts to gel. This makes it easier to sand.
Basically you will gouge out the cracks in a V shape with a dremmel, clean them with acetone, and apply enough gelcoat to fill the groove. The hard part for me is sanding the repair area, without sanding the area around it. Our Boler
is 45 years old and underneath the tarnished layer of gelcoat is a very white base. If you sand too much you end up with a white area around the colour matched one you just made.
A word about catalyst is you need to figure out what ratio works best for your climate. All the videos are specific to Florida and boats. Hot and humid. In Calgary I find a higher ratio than the 2% they recommend works better. Most of the mixing tables only go down to 18 degrees celcius. ha ha ha That's a heat wave here. 3% works better in my massive 2 months of experience.