Hi, 
I recently started using a compressor in the master buss. I have Slate Everything Bundle so I'm trying out the included buss compressors which are really nice. But they are now soon 4 years old, and there must be new ones worth trying. Can you please recommend plugins for this purpose? 
I compress very lightly, around -2, -3 db, But also for the colour. 
Genre guitar based rock/ballads.

T-Racks bus compressor is a good one.....demo it and see what you think.

PC4K bus compressor, T-RackS, Waves Gold has some nice compressors too.
 
If you're looking for color you'll want a variety ... next stop is the Deals forum

I guess if you're looking for a "Track" bus compressor, the 
above are great recommendations, and there are many more,
Including Waves SSL Bus Compressor, SSL Duende Bus Compressor,
etc...ad nauseum, just depending on "what you're after"
...if you're looking for a "Master Bus" compressor - Ozone 7 Advanced.  It's a 
one stop Master Bus/Mastering tool that is, IMO, AWESOME!

TDR Kotelnikov is a good free one. At the other end of the price scale, my current favorite bus compressor is the one in Acustica Coral, a package which includes EQ, preamp, and more for 200 euros. 
 
And +1 on the awesomeness of Ozone Advanced, which has several excellent compressors and limiters, including the really cool Vintage models. The only drawbacks are the frequently high CPU usage and the cost of the package when not on sale. 
 
Slate VBC isn't bad at all ... you already have three of the better options for bus compression out there. It's fun to try the competition, though. :-)
 
Cheers,
Eddie
 

Waves SSL. And the Waves SSL bundle is on sale for probably less than the price of 1 plugin.

the free Reaper compressor

Waves  API 2500 is my new favorite.
You will have to wait for it to go on sale though, currently too expensive.

I use The Glue most often on the mixbus, but lately I've branched out to the Waves SSL comp, which I sometimes like better than The Glue, though both are really similar. I've also used MJUC by Klanghelm which is also very good and punchy.

Thanks to all! awesome... I'll look into your suggestions. As Eddie said, it's fun to try :-)