Not sure if we are talking about the same thing, but I too am able to get into this "visual state".

I have started meditating a couple of years ago to better connect to my emotions and manage my ADHD and at one point I started seeing some colors (mostly yellow and green) and then a couple of months later it even became full-blown lucid states where I knew I am consciously awake, yet at the same time could view imagery and symbols that were deeply personal and helped me cathartically understand many things about myself.

But to your question - I have a recipe that works for myself, and I am curious if it will work for you too:

- ANC Headphones + listen to things like (Music for Psychdelic Therapy by Jon Hopkins)

- Ideally lay flat on a bed/ground, in a position where you can entirely relax all your muscles

- Cover eyes with a dark T-shirt or a pillow so that NO light gets in

- if you have trouble with nose breathing like me, use Nose strips (that helps for me)

And now the more challenging part, what happens in my head:

- consciously relax all of the muscles in the body, if I have some kind of pain somewhere, try to not think about it

- just as meditation goes, try to not think about anything, focusing on the music like I mentioned above helps. If some thought occurs, some emotion comes, really just observe it and let it pass. This is of course easier said than done, but I think it's very important to learn to not be always reactive

- to intensify the focus and for me, this is how the colors start (later becoming symbols), try to not even move your eyes while closed. Imagine looking as if on some object that is as close as 5 inches away from your face and don't move the eyes until you reach the "colors" stage

As for me, I start seeing colors and shapes around 10-20 minutes into this. But I am pretty confident that in the beginning before I realized this was happening, it took even longer.

I don't know if this will work for you, but I will be happy to answer any questions :)