I am in Kuwait where it gets very hot in summer (up to 50C). I plan to build my greenhouse using polyCarbonite. Can I use another color than clear to avoid the heat inside the greenhouse?
I'm rather wondering why you need a greenhouse in such a hot region, but regarding shading of greenhouses, you can buy green coloured shading, usually plastic or polycarbonate of some sort, see link for example
Bear in mind, though, that shading also reduces light levels - more information in the link below. Although its aimed at the UK market, the basic principles regarding methods of shading and cooling are the same
I've used a product called Aluminet here in Phoenix, AZ. It's a shade cloth available in a variety of shade levels. It reflects some light and diffuses the light passing through, so it' different than just regular shade cloth or greenhouse shade paint.
I've used 50% shade when growing cactus and it works quite well, in my opinion. I don't have a greenhouse though.