I am using Windows 10 20H2 and have upgraded to Audacity 3.3, 64 bit, but there is no change in the spectrogram colours and changing the settings in preferences always keeps the spectrogram blue under any selection.
I assume that you mean “Audacity 3.0.3 64-bit”.
Are you perhaps confusing “spectrogram” and “waveform”?
See here for changing the waveform color: https://manual.audacityteam.org/man/audio_tracks.html#colors
See here for the track spectrogram: https://manual.audacityteam.org/man/spectrogram_view.html