Honestly, I would order both and compare. You just cannot appreciate the color unless you do. If you like rich, velvety color that glows from the inside out, go kashmir. If you want more translucency and sparkle, go ceylon. The kashmirs aren't inky in the least and do not black out. They are blue, not navy. The faceting can be fully seen with decent lighting and the glow of the kashmir color is just so stunning.
I can tell you this, however: the color on the kashmir is so incredible that my original plan to use this for a bit and buy a natural sapphire in a year or so is down the tubes. I can't imagine I would find anything as nice as this in a untreated natural and I wouldn't want to give this up anyway. Yes, it's that good.
I believe I received a ceylon by mistake (you can see that post with pics in this forum) and just wasn't impressed; however, that wasn't because it wasn't pretty (it was!), but it was just blah compared to the kashmir.
Ok, now that you know my dislike for kashmirs HA, have fun deciding! I'm sure you'll love whichever you get!
This is what it looks like under a tree (it's in a stone holder lol). That's the glow that you see in any lighting. It's like it's lit up from the inside.
With what I believe is a ceylon (maybe a light ceylon), but it hasn't been verified yet. The smaller, more saturated stone is the kashmir.