I go to File > Save for web (plugin) > then enter custom height and width
My version 4.33 does not allow you to set height or width in the Save for web (plugin) screen.
I just took a 1600 by 1200 jpg image color 16,7 Millions (24 BitsPerPixel). and set width to 100pxs. and re sized. Final image is 100 by 75 px. thats 4:3 ratio and it has 16,7 Millions (24 BitsPerPixel) color in the web save reduction.
The amount of color and the image format will have an effect of the final image. but you get to see things before you ok the save. Don't know what your doing wrong. Please try my fist post again the way I said. If still no good can you post the original on a site like photo bucket and I'll make 100px max on a side.