How to send a command to a FFmpeg `color` source filter?

FFmpeg Documentation states:

The color source supports the following commands:

c, color – the color source filter

How can I use this command?

Thinking a standard sendcmd usage, I tried

ffmpeg -f lavfi -i sendcmd='1 color c blue',color=c=red output.mp4

I got slapped by

[lavfi @ 000001f4fefcbd80] Too many inputs specified for the "color" filter.
sendcmd=1 color c blue,color=c=red: Invalid argument

which makes sense because color filter does not take any input stream.

Is there some other way to make this work?