This filter is found in
Colormap Rotation lets you exchange one color range to another range.
Preview: This Preview displays a thumbnail of the original image and another one displaying color changes interactively, before they are applied to Image.
This tab deals with main options.
The Color Circle: Two axis to define "From" range. The curved arrow in angle lets to recognise "From" axis and "To" axis of range. Click-drag these axis to change range.
Switch to Clockwise/Counterclockwise: Sets the direction the range is going.
Change Order of Arrows: Inverts From and To axis. This results in an important color change as colors in selection angle are different.
Select All selects the whole color circle.
From and To boxes display start axis and end axis positions (in rad/PI) which are limiting the selected color range. You can enter these positions manually or with help of arrow-heads.
This section options are the same as "From" section ones.
This tab deals with miscellaneous options.
In the "Misc" tab, you can specify how to treat grey colors. By default, grey is not considered as a color. But all colors, when they are very desaturated, look like grey, and you can tell filter to consider grey as a very desaturated color which will be affected by rotation.
What is Gray?: You specify there how much saturation will be considered grey. By increasing progressively saturation, you will see an enlarging circle in color circle and enlarging selected areas in Preview if Change To This option is checked.
Hue and Saturation: You set here the color you want grey to be transformed to. You do that, either by entering values into input boxes, or by click-dragging the small central circle in Hue/Saturation circle.
Mode: With Treat as this option, there will be no change in preview, selected "grey" areas will take the selected color and a rotation will be performed on image. With Change to this option, the selected color will be applied to "grey" areas and will appear in preview but no rotation will be performed.
Continuous Update displays color changes continuously in Rotated preview.
Zone: Entire Layer works on whole layer. Sélection displays selection only, Context displays selection in image context.
You can select here the angle unit used to locate colors in Hue/Saturation circle.