Patchwork patio - Mixed paving

[Bramble]

Hi.
I want to cover an area of concrete (approx 29 cubic metres) with a patchwork of slabs, quarry tiles, cobbles etc.
From what I've read (a lot, but still confused!!) it seems best to lay paving on top of concrete on a 50mm bedding mix of between 4 and 6:1 sharp sand:cement and then either joint it at the same time, for max strength, or later, with a 3:1 sharp sand:cement mix.
I have a couple of queries though....first, I want to colour, at least, the joints, with pigment, so wouldn't it be better to bed and mortar separately in that case, to avoid the expense of colouring ALL of the mix? Especially as I want a pale-ish mortar, so might need to use white cement, which will be dearer than OPC.
On the other hand, if some of my paving is quite shallow, surely it would be better to bed and mortar it at the same time?
Secondly, if mix ratios are calculated on a volume basis, why does everyone sell aggregates by the KG? I realise wet sand probably weighs more for the same volume than dry sand, but, if I'm to order my sand in bulk, how on earth am I to calculate how much I'll need. Sorry this is such a long post, but I don't want to order too much sand and then have my driveway look like a builders yard!
Any help and advice will be very greatly appreciated. Thank you :O :O

[lutonlagerlout]

use a small bucket (10 litre paint pot etc) for gauging your bedding
if bedding onto concrete you may consider a bond bridge or primer slurry to add adhesion
most professionals would rather bed onto type 1
your pigment will almost certainly fade!
anything else just ask
LLL