/usr/share/plplot5.9.9/cmap1_highfreq.pal is in libplplot11 5.9.9-2ubuntu2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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v2 hls 2 0. 240. 0.3 0.5 1. 0 1. 240. 1.0 0.5 1. 0