/usr/share/gwyddion/gradients/Rainbow2 is in gwyddion-common 2.47-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 | Gwyddion resource GwyGradient
0 0 0 0 1
0.25 1 0 0 1
0.5 0 1 0 1
0.75 0 0 1 1
1 1 1 1 1
|