How do I achieve this effect in colours. I've seen similar effect on Halsey cover art as well. Proficient in CC so hopefully it shouldn't be too hard, just thought I'd ask here first.
This is very likely a gradient map, which allows you to map different colors to the luminosity of a given picture.
There's more than one way to apply a gradient map:
Select the desired layer, then go to Image → Adjustments → Gradient maps. This is destructive.
In your layer palette, click the Fill and adjustments button and select Gradient map. This will create an adjustment layer, which you can put on top of the layers you want to affect. It can also receive a mask to control its effect. This is what I do in the following steps:
Then, I applied a gradient map that gives a rich red to the darks, tapers off to the grayish magenta you see on lighted columns, and I isolated part of the highlights range to get the blue-green. Absolute whites go back to a light magenta tint.
Note that the original picture probably had "real" whites, which were then mapped to a slight gray. This would make it hard to recover the right luminosity for the sake of this demo. Here's how I defined my gradient map:
The leftmost colours will replace the blacks, the rightmost will replace the whites.
Here's the result with the gradient map applied at around 50% on my quickly grayed-out source:
Keep in mind that ideally, you also do some manual adjustments in the end.
Here's a quick method to get you started. To get the polished look (like in your example) just spend more time on your masking to get a more mixed selection that will come across as more professional. For reference, I made this example in about 5 minutes.
Step 1: Get your picture!
Step 2: Duplicate your background layer (in case of royal failure) and start selecting the highlights of the image (or whatever pieces you want to turn blue in this instance). Again, this is where you want to spend some serious time to achieve the professional look.
Step 3: Use the hue/saturation layer adjustment, check 'colourize' and select the hue you want (cyan in this case). I also played around a bit with the saturation to get it to where I wanted it.
Step 4: Select the base layer and use the hue/saturation adjustment layer again. (Don't worry about selecting the inverse since we'll leave this layer under the blue one). This time we're colorizing with red.
Step 5: Add any additional adjustments you would like on the image and save! Here, I added some slight adjustments via 'levels' to darken the image slightly. You may want to play around with other adjustments and blending options to achieve the final look you want.
I know it's a basic tutorial, but hopefully this answer gives you what you need to get started on your image! Any other questions, feel free to ask away!