Adding Color Map to MrSID Imagery using QGIS

I am trying to convert a single band (grey) MrSid image to a 3 band (RGB) GeoTiff image. Using QGIS (3.12.3-București) on Windows 7, I saved it as a GeoTiff, which now has the 3 standard bands. Each is 1 to 255 min-max. However, the new GeoTiff image is still grey in color. The source from which I obtained the original image has 2 jpg files (1 is a low-res, grey overview), the other says it’s a "layout" file and when viewed, just shows what appears to be the image of a form, though it does have the 3 RGB bands (I’m pretty sure it’s not a color map). There are several xml and an shp file as well.

Is there a way to colorize the GeoTiff so that it appears more realistic?