Well... As you know, a ladder consists of 2 parts: a brush with the image of the ladder and another with the func_ladder...
Nice, turn the picture brush into a FUNC_WALL (if you haven?t done yet) and in its properties look for the RENDER MODE and set it to TEXTURE. Now, in the FX AMOUNT set 255... You?re done.
With this property, you get the blue color to be rendered completely invisible...
Now you could divide your image-brush-ladder in 3 parts: one for the steps and the other two for the sides, so you can see them in a more realistic perspective... If you need help just ask for an example map :).