I would like to use a set of color ramps that are available at CPT-CITY but cannot find any way to import the downloaded files.
Note that I have found the Catalog: cpt-city option under the Create New Color Ramp selection. However, the ramps that I'm interested are not found in this collection.
Is there some way to simply browse to the file that I'm interested in to register it with my QGIS project?
The solution proposed by @Xi Jin is available for raster layers only and is for color maps, not color ramps. Even though very similar, the concepts are different: a color map assigns pre-defined colors (could be a color ramp) to certain values (numbers or classes) - like assigning elevation data to a topographic color ramp: 0 to 200 m: green; 200 to 500 m: yellow; 500 to 1000 m: brown; over 1000 m: white. Thus color maps are a more narrow concept: color ramp are just ordered gradients of colors, without assigning actual values: green, yellow, brown, white. See also here for color maps: https://pvanb.wordpress.com/2014/02/05/creating-a-qgis-color-map-from-text-file/
The standard way to import color ramps from a file or a URL is using Menu Settings / Style Manager, where you have a button to import/export files - see documentation for Style Manager. The color ramps you add in this way will permanently be available everywhere in QGIS.
If you want to create your own color ramps, click the green + symbol. You can add a Name and Tag(s) for the color ramps created to be easier to find/identify them when you have a lot of color ramps.
Color ramps created in this way can be exported (to share) again with the button on the left.
For all color ramps you create or import, set the checkbox Add to favorites for those color ramps that you want to be added to favorites. They will be immediately visible in the drop down list when selecting color ramps - all others are hidden behind All Color Ramps:
Assigning names and tags helps you to keep an overview of your color ramps and other styles.
By the way, the style managar can be used in the same way for other styles like composed styles for vector layers (points, lines, polygons), for texts/labels, legend symbos and 3D symbols. So it is a powerful tool to create and administrate everything connected with styles.
You can load color maps from "load color map" button. Look at the picture, it is in red circle.
After rephrasing my question a little, I found this answer to a similar query.
The problem was that I could only import XML files, and I didn't know how to convert from CPT to XML. It should have been obvious to simply export an existing ramp as XML, modify it for the values i wanted, and import as my new ramp.
The CPT that I wanted has stops, not in elevation, but of the form 0, 1, 2, .. 125. These need to be between 0-1 for the XML. The CPT has 126 lines, so I updated each to be $line-number / 125 and it works reasonably ok.
The XML wants them concatenated as one long value of a single tag. eg.
STOP;R,G,B,A or 0.4206;189,175,198,255
Each of these sets should be concatenated to the next with a colon (:)
This document has directions on adding color ramps from the cpt-city website towards the end https://psqgis.org/downloads/QGIS_3.4_color_ramps.doc
