It's more closely tied to video memory. With a specific amount of memory,
you can get either high resolution at low color depth, high color depth at
low resolution, or some combination (I forget the actual formula.)
Most modern video cards will handle pretty good color depth at high
(1024x768 or above) resolution. Which Gateway model, and how much video
memory does it have? Looking on Gateway's support site, the monitor (19 inch
diagonal, 18 inch viewing area, SuperFST tube) can reach a maximum
resolution of 1600x1200. The Video Electronics Standards Association (VESA)
1,600 × 1,200 at 75 hertz (Hz) mode is the prime mode.
Quick search found this site with relevant info:
http://www.mtechlaptops.com/video_memory.htm
Here's how much memory you need to run true color at specific resolutions:
1024X768 @ True Color (32 Bit) 25.1MB
1400X1050 @ True Color 47MB
1600X1200 @ True Color (32 Bit) 76.8MB
So if that gateway's only got 8-32 Mb video RAM (and many models with shared
memory will only GIVE 8 Mb or so) you're not going to hit true color, and
will need to replace the video card with one that's more powerful. 128 Mb
GeForceFX 5200s (new, DX9 compatible) start at $99....