How do I generate lots of sprites at faster rates?

(My question may sound out of league)

I am working on pixel coloring game (one of my example:-

play.google.com/store/apps/details No need to download. Link added to get an idea of what I am talking about)

There are approx. 30000 boxes to be colored. I have optimized game in such a way that whole thing works smoothly. But there is a grave issue which is hitting me

To generate 30000 boxes, it initially takes around 10 seconds to do that. And that is HUGE time to scare away the users

So

1.) Is there any way to optimize this 10 seconds

2.) Any other workaround (example:- do 'this' in such a way that whole thing look optimized)

Thanks in advance

I did a quick test using drawing canvas snapshot to read the rgb values of the image and then I create a tilemap with over 30k tiles based on the rgb data of the given pixels.

Took only a second to generate (including the async snapshot).