I would like to change the colors of the Reference grid, both in the perspective and ortho view. I am editing my 3DSceneColors.bw file and nothing I am doing seems to have any effect. I have tried the text below and again, no change at all.

OrthoGridColor: 0.25 0.25 0.25 # ortho viewport grid lines
OrthoGridOriginColor: 1.00 0.0 0.0 # ortho viewport origin lines

I would love to be able to change:

The origin grid color, as well as have different colors for the grid and the grid spacing.

Any help would be great.

Leaving this here for for others to find,

You are able to change the color of the grid by editing your 3DSceneColors config file.
By default you dont have a "3DSceneColors.{theme}" file in your "{user}/houdini/config folder".

The easiest way to create this file(s) is to open the houdini help and search for "Viewport Color Editor", then open up the link that refers to python panel example, then press the load button to load the panel.

This panel is an interface that creates / edits the "3DSceneColors.{theme} file". From here you can go wild changing colors and such.
Specifically the referece grid color property is called "GridColor" both in the editor and in the file.

Some extra info
Each theme (light, dark and grey(bw)) have files that edit their respective themes. Once you hit the save button on the viewport color editor panel it creates a file specific to the theme. So if you change the colors in light mode then switch to dark mode, houdini will reference the dark theme file and not display your previously chosen grid color that was saved in the light themed file. This is what normally throws people off.
You need to restart your houdini for houdini to reference the color file, just make sure that you are viewing the same theme in houdini as the color file that you are editing.

Hope this helps someone in the future.

The Color Panel didn't open here as well when pressing "Load" in the help files.

But I figured out a way, so just in case anyone else runs into this:

Open a new floating panel and set its type to "...misc>Python Panel". Then you can select the "viewport color editor" with the dropdown menu at the top, but only after you hit the "Load" button in the help files. Seems this code is not loaded by default somehow.

With this color panel you can edit the viewport colors, and if you don't want to restart Houdini after every edit, open the Display Options panel as well and toggle the Color Scheme after every save in the Color Editor.

I noticed that the editing works in a strange way, one would expect this to be straight forward but it seems all the currently active fields are adjusted when changing a single specific color. So you have to disable all the fields you already adjusted , before adjusting the next color.