Why is Red Lead Paint Orange? 

Not the artists' pigment, but the red lead paint that was used
historically on the structural steel of bridges and steel-framed
buildings. It seems to be orange, not red.  Same with the red lead
paint still applied today on wooden boats. It's orange, not red.

Is red lead as a powder colored RED, but when mixed as a paint it
becomes ORANGE? Why is Red Lead Paint Orange?

Technically Red lead paint is not orange ,it should be salmon pink .
It mainly consists of Pb3O4 and PbO,Its colors range frome orange red
to red, according to the ratio of Pb3O4/PbO.