I can't speak specifically for hatch covers, but I know that when I come to the boat, and remove the blue wheel/pedestal cover, the top of the pedestal guard is so hot, that I can't touch it. So I think your concern for the heat is valid.

Next time around, I'll probably have at least the bimini made from a lighter color; light blue, tan, etc. It gets hot under the bimini from the heat it absorbs. Once I figure out how to use a sewing machine, I plan to make a light colored awning to go above the bimini and dodger on those hot, still days.

We use an Oyster color (like a light gray) for our hatch covers. I can't say how much better they are over a dark color, but they blend in nicely with the gelcoat color. I consider our navy bimini, sailcover, and headsail cover to be sufficient "accent" color for our boat.

The PO on my boat used a thermal lining under the canvas (blue) hatch covers. Boat is in Miami and the inside is much cooler with covers on. Have not noticed any high temperture on hatch with coverings on. Just had new elastic put in covers and while they were off the boat, heat was extreme below and hatchs were hot. To expensive to keep the a/c running all of the time. Just put in a couple of fans below and plugged them into ac outlets. :cool:

Someone else on either this forum or perhaps on the other email list once posted the idea of using the foil bubble wrap.
I happened to have had some and tried it- works great at reflecting the heat out at both the cabin top and v berth hatches.

It is cheap, easy to cut to shape, and for now, saves me from making exterior covers. They just tuck right into place- no need for velcro or anything.

Just thought it worth passing this on. I cannot recall who first posted the idea.

My hatch covers all have internal padding to reduce the heat. The PO had this done and it worked well for me on Lake mead in 100 degree plus days. The padding is the type of stuff they use for filler in warm jackets. The companion way hatch has a similar cover with lead weights on the end to hold it down.
John Meyer 2135
San Pedro, CA

I bought a couple of auto windshield shades, cut them to fit and place them between the screens and closed hatch, (silver side up). Works well, cheap and no labor.

Wally,
The windshield shades will work well for keeping sun and heat out of the cabin, but it won't help with the possible UV degradation of the Lewmar hatches.

Laura,
when i purchased some new cabin side windows (mark I no opening ports). Mark from Mark plastics warned me not to put anything on right next to the plastic windows as it would cause the heat to build up and degrade the plastic faster than normal. I would think he would know something about that since he manufactures the windows. when i just placed the foil bubble wrap directly over my opening hatches it left some type of silver residue although it may be a bit warmer in texas than up north. FWIW