I know from experience that,if you want black weights you’ll have to ask and,most places will have to order them in.
As for the position,if they put them in any other position than what the machine says,they will be out of balance.
When I had new tyres fitted last year, I asked the tyre fitting place I went to if they would fit non-corroding weights, as I think that rusty balance weights look unsightly. The weights they fitted look as if they’re zinc plated, so I’m hoping they’ll be a bit more resistant to corrosion than the ‘standard’ weights are. Time will tell............
Agree that removing the weights and re-positioning them behind the spokes wouldn’t work as the wheels would no longer be balanced. @Borbus; paint them black if you want to conceal them.
Interestingly, when the wheel barrels of VW’s factory wheels are black, VW don’t fit black balance weights in the factory either - the weights they use are a very light grey colour. They are pretty resistant to corrosion though.