Kilian Noorlander

I think you need to learn about attributes. They can help you drive almost all of the things relevant to this question..

In practice:

Points on a grid.
Points are white
Bouncing ball is blue

Attribute transfer "Cd" from ball to points.
If you want there to be a fade, add a trail sop, you can even choose the duration of frames..
Copy to points, boxes to points.
Resulting boxes have same color as points, as far as I remember.

In Solaris / LOPS -> karma material: geometry color, to import the color from SOPS to LOPS.
You could also use that to control the glow of the boxes, since black is 0 and white is 1 ( which can be used to control many shader properties and attributes (like roughness, glow etc.)
You could start your setup in SOPS with black and white, instead of blue and white and then when bringing that into your Karma material, with "geometry color", you could adjust the color with a ramp, to whatever you like.

Geometry Color:

https://note.com/ryokucharyoku2/n/n6e82d801c927?hl=en [note.com]
https://www.sidefx.com/docs/houdini/nodes/lop/geometrycolor.html [www.sidefx.com]

Karma Ramp:

youtube.com/shorts/msbr4n8qel8

More in-depth videos on making Pong and attribute transfer. Quite similar to what you want, I think:

youtube.com/watch?v=pxSqt7_hoOs
youtube.com/watch?v=p_Z1eC1jjPY

Lights maybe:

sidefx.com/docs/houdini/solaris/support/geometry_lights.html
sidefx.com/docs/houdini/solaris/kug/lights.html

There is a setup for Karma in the content libray.
There are two .zip files - you can just download the smaller one (1.3GB).

https://www.sidefx.com/contentlibrary/polar-camera-clouds/ [www.sidefx.com]

In multiple sessions I noticed that "Kill" in the Render Manager does not work, at least not on my machine, in H 20.5.278

Additionally, it no longer shows render progress, only N/A or 100%