Painting the summit of Mont Blanc red

It really depend on what kind of method he would use for painting it - some paints are more toxic then other. In the past few years there has been a lot of development in non toxic paints, but still, I guess that a large amount of any type of paint is not contributing to the environment. 

I suppose that the governments of France and Italy would have something to say about it as well,  I can't see how either of them would want to get all that snow painted.

I guess the best solution would be to do like Cristo  and cover it in fabric in some way. In his NY exhibit of the orange arches he used a recycled plastic fabric and after the show was over, he cut the fabric into small pieces and sold the pieces, if I'm not mistaken, some of the money was donated to environmental organizations.

lilly pretty much covered the subject of toxicity. There's also the subject of the color: snow returns almost all of the light because it's white, but if it's painted red some of the radiation will not be reflected back, and instead it will heat up the snow. I don't know what's the temperature there, but if it's not too high the paint could cause the snow to melt.