Hey man, if you look closely at the picture the pink hue is just from the LED lighting above the plant. As far as I know there is no additive for enhancing colour but there are a few alternate methods to grow some colourful beauties! First and easiest method is choose a strain which has colourful genetics, things crossed with blueberry generally have the potential to produce purple/blue tints. If you check out my first grow journal its a Northern Lights crossed with Blueberry and I managed to get some nice colour on her. There are a lot of strains out now that are bred primarily with bag appeal in mind with amazing colours, sweet seeds have some nice options for red/purple/almost black buds. I'm growing a Nirvana Northern Lights right now on day 40 and theres no sign of colour yet, but she is in a tiny 16oz pot so not expecting much from her.
With all that in mind you can help the colours come through on your leaves with lower grow room temperatures, obviously not cold like a fridge because that can stunt growth, but it's proven that cooler temps encourage the colouring to show up - easier to do with LEDs as apposed to HPS.
Kinda rambled on there but I hope some of it helped..one last thing: always check out grow journals when choosing a strain, they will give you a much more accurate idea of what your plant will look like compared to the breeder's image - very often they're edited to look very appealing.