I want to save shapefile (polygon) with color in gmt format and in geoghrapic coordinate not UTM. Mmy shapefile is in UTM. I run below as an example how to show in lat lon and with color.
ogr2ogr -f "GMT" Hudson_bounds.gmt Hudson_bounds.shp
Problem 1. Shapefiles don't store color. That's usually stored in the program using them.
If your data is in UTM, re-project it to Geographic (wgs-84) before you convert it.
Use ogr2ogr or an on-line converter to convert the shapefile. https://mygeodata.cloud/converter/shp-to-gml
This link might help... How to convert *.shp files to *.gmt format type files?