The 32 in _NEWIMAGE(Width, Height, 32) means you are in the land of _RGB32(red, green, blue) colors.
Red, green, blue run from 0 to 255,
_RGB32(255, 0, 0) = color #12 in 0-15 color numbers, yellow _RGB32(255, 255, 0) see _RGB32() for more.
Another way to command colors in 32 bit color mode is Hexidecimal &H FF FF FF FF
the first 2 FF are alpha or transparency FF is fully opaque 0 is fully transparent
the next 2 FF are red levels
the next 2 FF are green levels
the next 2 FF are blue
_NEWIMAGE has many screen modes other than 32, you might like 12 with 256 colors (if read the help file correctly)