This "Chromatic Aberration" tool works on the image before demosaicing, that's why it's located in the Raw tab. The Chromatic Aberration Correction tool in the Transform tab works on the image after demosaicing.
Chromatic aberration correction on the raw level is currently only supported for raw files from cameras with a Bayer filter. If you need to remove chromatic aberration from raw photos from X-Trans sensor cameras (Fuji), then use the Chromatic Aberration Correction tool in the Transform tab.
Chromatic aberration can be corrected by using the "Red" and "Blue" sliders. Normally you won't see any chromatic aberration in the fit-to-screen preview, therefore it is highly recommended to open a detail window or to zoom the main preview in to 100% File:Gtk-zoom-100.png or more when you attempt this kind of correction.
This tools corrects bluish-green and magenta fringes due to lens lateral chromatic aberration that show mainly in the borders of the image. This correction is performed before demosaicing and can sometimes improve the quality of demosaicing.
If "Auto-correction" is checked, the "Red"/"Blue" sliders are disabled and an automated detection and correction of chromatic aberration is performed. Where manual correction applies a constant value across the image, auto-correction divides the image into many blocks and tailors the values required to eliminate chromatic aberration to each block. For this reason auto-correction usually performs better than manual correction, and the auto-correction values cannot be displayed in the sliders.
If the "Red"/"Blue" sliders are non-zero the given values are used to correct chromatic aberration. They cannot be used at the same time as "Auto-correction".