How can I get a higher color mode?

Your computer should be using high color mode by default. If it isn't make sure you have it enabled in your display properties.

Windows 95/98: First click on the START button then hover the mouse over Settings and then click on Control Panel. Now Double click on the Display icon, click on display settings, there should be a slider for your resolution and a drop down box for color, select the resolution/color depth you want.

Windows NT/2K/XP: Right click on the desktop(not on an icon or taskbar), select properties, go to display properties, select display propteries, select the resolution/color depth you want.

Windows Vista/Windows 7: Right click on the desktop(not on an icon or the taskbar) select Personalize, Select Display Settings, Here you can now choose the resolution/color depth you want.

Also make sure you installed the device drivers for your video card(they are found on the manufacture of the video card's site)

NOTE: If your resolution drops, this is due to your video card not having enough video memory for the resolution/color depth.