Okay so my Lusta was my first ever hair topper bought online, and the colour was a gamble. Trust Fund Baby, a dark brunette with light and medium brunette and blonde highlights through it. It paid off, but it wasn't a blind gamble, and the reason why is worth passing on.
A woman in a Facebook group gave me the tip. If you don't know your colour, buy one with several tones in it. Highlights, lowlights, a bit of dimension. If there are a few shades running through the piece, your own hair will match at least one of them, and the rest reads as natural variation instead of a mismatch.
That's exactly why I picked Trust Fund Baby. It's more or less every shade of brunette at once, light through to dark. I was around an A2 at the root back then, with a fading balayage on the ends I was growing out, so something in there was always going to catch.
It worked. But do both things, not just the one I did. Pick a multi-tone shade and message the brand for a proper colour match too.
If you're in the UK, budget for customs as well. Mine came from Australia and I paid roughly £60 to £70 on top before it was delivered.
The six month and ten month updates are in my Lusta hair topper review, and all eight toppers I've worn are compared in my best hair toppers UK post.