wow, you beat me
by seconds with the exact same wording
edit: actually all except the first are really excellent! the first one is good, but a little tame compared to its neighbours

Thanks guys

I agree, the first one is the one I worked only 5 minutes with the gradients.
The 2nd one is the first I made using this technique with the 2 layered coloring formulas. I like its "comics" aspect.
My favourite is the 3rd. I like the flashing colors.
The 4th is nice too because there are a lot of details, but the gradients could be better.
Approx 1h of design by image : to find the right location (mostly by zooming in a more or less large minibrot's elephant's or seahorse's valley first, then finding a minijulia in a 2nd level minibrot's antenna or deep in the middle of seahorse valley, then finding the right color density and the cool gradients)
And say 15mn to 20mn of render on my poor laptop...(BTW I just bought a laptop cooling pad because of too many crashes because of CPU overheating

)