This is such an amazing Haiku. As I always say within a haiku the imagery needs to be forefront. The description between the title and the poem itself, is perfect.

The main point of the poem is a red maple tree, which already gives the reader an idea of the imagery and the season you are writing about. I see it as being autumn and leaves are starting to fall off all of the other trees. As you said in the first line, this one red leaf tree stands above all. Usually in the first line you want to make it the plot point and you have done so here.

The second line is perfect because you added a description about the plot point itself. There is a tree that is all alone, and that tree stands above all because of the color it portrays. It stands tall because of the color against the blue sky. I love the blue sky line because it enhances the tree and the poem itself.

The third line lets the poem breathe and it is a great wrap up, because you want to make the plot live and you have done so. Above all the tree is enhanced because it is ablaze in the sun.

I wouldn't change anything about the poem itself, and I am going to nominate later if I can!