I'm not familiar with the new
GW product scheme, so stick with me, I'll use base terminology rather than product names.
As was already iterated, keeping the wash color similar to the color in question will usually work fine. The darker the wash, the more contrast you'll cause, to make the detail definition more extreme.
But, the darker the color in question, the darker the wash will have to be to stay effective. For your purple marine I would agree with TheMeanDM and say use a black wash.
For lighter colors, use a wash of the same color family. Yellows, golds, oranges will usually use a brown based wash (sepia,
raw umber, burnt umber, etc). The more subtle you want the effect, the more you'll thin it down. More extreme desires? Don't thin it as much, if at all.
It takes a little practice, but you'll get it. The 3 washes you'll probably use most often are a Black wash, a darker brown wash (for weathering and general "Grime.") and a mid-range brown wash (for yellows, golds, browns, etc). All other color washes (blue, green, purple, etc) will typically only really apply to those particular colors (or grey, to somewhat "tint" the area).
Also keep in mind, you can use multiple applications of multiple washes, if you wish. As an example: apply a darker brown wash all over a surface, allow to dry, then apply a black wash in only the lowest recesses, for a deeper gradient of shading.
Might I suggest a video?
https://www.youtube.com/watch?v=HCAx_mpZD1w And, being that you've such a low post count, and you're asking a fairly early painter question, here's a video on drybrushing, another building block for our hobby:
https://www.youtube.com/watch?v=aRLsaXGHPfc Hope I helped, good luck