Making color text file using GDAL?

I have an 8-bit greyscale image that I want to convert to a “heat map” based on data values (0-255), using a color ramp. I’m aware that gdaldem works with color-relief, so I used the following steps from a prior post:

1. Take a raster of your choice (like SRTM as an example)

2. Create the following text file named col.txt:

   0 black
   100 blue
   200 yellow
   300 orange
   400 red
   500 white
   

3. On command line, run

   gdaldem color-relief N51E007.hgt col.txt out.tif
   

   When I do this, I get the following:

   "ERROR 1: Unknown color : Menlo-Regular;}"
   

It seems it is seeing the font type, for some odd reason.