/usr/share/plplot5.10.0/cmap1_highfreq.pal is in libplplot12 5.10.0+dfsg2-0.1ubuntu2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4
v2 hls 2 0. 240. 0.3 0.5 1. 0 1. 240. 1.0 0.5 1. 0