Actually this sounds similar to what accidentally happened to me when I tried to do Vipassana meditation to get to sleep. If you want to do it on purpose, then I recommend Vipassana, based on my only one experience. The moment that it happened I think I was thinking about how the body is only temporary, including feeling my arms etc, but I was just watching and waiting to go to sleep not expecting something to happen.

I put a separate post about it here asking for advice how to sleep like normal now because I didn't like it happening unexpectedly.
The only difference is I saw a vortex and then popped into a void, but you saw colours and shapes instead, so maybe different.

I found another thread here which seems kind of similar too, but he did it when he was already in a dream.

I'm curious if there's a name for this observe-going-to-sleep technique so I could look up more about it.