The problem is there there is no similar colour in the colormap. Using your 72 colour palette for indexing, the colormap is a good match.
However...
The available indexed colors do not have anything close to the blue in original RGB image so it uses the nearest. You can select from the colormap and you can paint or fill that selection but only using the colours in the colormap.
edit: I painted in a bit using that lighter blue (and a bit in yellow) as an example.
However...
The available indexed colors do not have anything close to the blue in original RGB image so it uses the nearest. You can select from the colormap and you can paint or fill that selection but only using the colours in the colormap.
edit: I painted in a bit using that lighter blue (and a bit in yellow) as an example.