Do you own the blue property or the red?
I would think red would have to remove the leaves to somewhere else on his property. Of course, red could do nothing and let nature blow them away. Although blue may not be happy with that solution, I don’t see how it would be illegal (littering).
I would think snow is a different story. Since snow melts, I don’t see how it would be littering to blow snow on the neighbor’s lawn. As long as red does not damage any of blue’s property (broken bushes, messed up landscaping, dented vehicles, etc) or creates a hazard (blows snow on blue’s driveway which blocks the driveway), I don’t see how it would be illegal (or un-neighborly) to blow it on blue’s property.
Regarding the ownership of trees, I have read that the portion of the tree that is on or over a given property belongs to the respective owners. Therefore, if blue had a line of trees on his property along the property line, red could trim the trees where it crosses the property line. The only caveat is that anything red does to the tree can’t kill it.
One more thing, if red and yellow own the properties where the driveways are located (the drawing suggests that), the properties are commonly called flagpole lots. Therefore, I doubt if there is an easement to allow access to the red or yellow property. The pole for my flagpole lot is 20 ft wide for a 10 ft driveway.