The 32-bit and 64-bit editions are for different processors and the 32-bit version is the one you need.
Anyway, cursors can be in different format and the format determines the number of colors and the size of the cursor file in kilobytes.
You have probably opened a cursor in a format that only allows few colors and the application is trying its best to represent the color you are trying to use with the colors available. I would recommend to open the cursor, then insert a new image in 32 color depth, copy contents of the old image to the inserted one and the delete the old image from the cursor.