Image Modes
It's a feature found in all photo-editing applications but one that rarely gets a mention. Most photographers work in RGB mode (Red, Green and Blue) - the color mode used by both the camera and the computer monitor. Professionals working in print, using Photoshop, will inevitably work in CMYK (Cyan, Magenta, Yellow, and Black) mode. We don't have this in Elements.
Most photographers will only ever use RGB mode, but occasionally might encounter a file that doesn't edit properly, so it pays to check its mode status. Choose Image>Mode>RGB Color (menu on the left) to convert it to a full-color file, or if it's a 12 or 14-bit file, choose the 8-bit conversion option. Elements does not work with anything higher than 8-bit files. Other modes under the Image>Mode menu include Grayscale, Indexed Color..., and Bitmap....
Grayscale: RGB files have three color channels, while grayscale has one: grey. When you convert from RGB to Grayscale...