Search from any folder, and select an image in it from a dropdown menu; assign the desired width, and height is calculated accordingly (proportions can be unlocked, but this is optimized for most use cases).
Colour is assigned by either picking up the real RGB values from the underlying image, or by forcing a selection of colours (palette); in this case the default palette is based on an automatic reduction of the available colour range, and they can subsequently altered for the desired effect; the default palette could also represent an arbitrary pre-loaded catalogue, or even be assigned with an eyedropper tool. When using a palette, the underlying RGB values convert to the most similar colour in the defined range.
In most cases, working with rhinestones, studs, and other accessories with a limited colour selection, "palette" is the common choice; however, "RGB" can come in handy for work that integrates printing techniques.