These popups, which you get by clicking on a color box on the main window or in certain dialog boxes, allow you to choose a color by clicking on it. There are two color pickers, and you can choose which one to use with "Use HSL color picker" on the options menu.
The HSL (hue, saturation, lumination)
color picker is shown on the left. It displays the colors with
brightness increasing as you go down, hue changing left to right
and saturation increasing to the right. It displays colors in a
more natural fasion than the RGB color picker.
The RGB (red, green, blue) color picker
is similar but arranges the colors differently. It shows 16 small
boxes of color, with red increasing to the right and green
increasing as you go down. Each box has a different, constant
blue value.
Both color pickers allow you to choose transparent (0,0,0), black (0,0,8) or white(255,255,255).
On the left side, the six currently selected colors for line, fill and text colors are displayed. Below that, the ten most recently used colors are displayed.
You can click Use Texture to bring up the Choose Texture dialog box:
This will allow you to choose any open
file (except the current one) to be used as a texture (that is,
drawing will be performed with another bitmap instead of a solid
color). If you haven't opened any other files, a File Open dialog
box will be opened instead so you can choose a bitmap. If you
want to load a file to use as a texture, you can do so by
clicking Load Texture File. Again, this will
bring up a file open dialog so you can load a file.