Are you in the US or the UK? Or Canada? The devices available will vary, so I just want to be sure.
Hue
Probably the easiest choice is to just get the Phillips BR 30 bulbs. These do color changes. You will need one Phillips hue bridge (either the round one or the square one will work, but the square one is the newer generation and will also work with HomeKit) for each 40 lights as well. (A bridge can actually support 50 devices, but that leaves you some room to add switches or motion sensors.)
These are officially supported and work well.
https://support.smartthings.com/hc/en-us/articles/200848024-How-to-connect-Philips-Hue-devices
https://www.amazon.com/Philips-432690-Equivalent-Single-Light/dp/B00HNLQQ7K/
Osram Lightify
Another alternative is to get the Osborne Lightify recessed kit. It’s a complete kit and does do color changes. If you only buy one it costs about $50 per light but you can bring the cost down by buying multiples. I’m going to give you the Amazon link so you can look at the device, but you might be able to get a better deal elsewhere if you are buying a lot of them. If you are using them with smart things you do not need the Osram Lightify “gateway” although if you get one you will be able to update the firmware on the lights, so it’s up to you. Most people using SmartThings don’t get the gateway.
https://www.amazon.com/SYLVANIA-LIGHTIFY-Osram-Recessed-Smart/dp/B0196M601A
This device is also on the official “works with SmartThings” list.
https://support.smartthings.com/hc/en-us/articles/214191863-How-to-connect-OSRAM-LIGHTIFY-Bulbs
Dumb bulbs, smart switch
If you don’t need color changes, it will be both simpler and much less expensive to use regular bulbs and just get a smart switch. So it really depends on your own requirements.
Smart switches to go with smart bulbs
The one thing you don’t want to do is to combine a smart bulb with a regular smart dimmer switch. The two devices will confuse each other. Fortunately, there are a number of alternative methods for using a switch to control smart bulbs. If you want color control, at the present time the easiest way is to put a Wi-Fi phone or tablet on the wall. If you just want to switch to do on/off/den and control color through automations and your phone, then there are a number of good options:
So there are lots of different choices, it just depends on your budget and your own preferences. Just know that if you want color changing bulbs that’s going to at least double your cost and maybe more. 
