First, gather ye rubber gloves, damp fabric, cooling racks, dyes...
Then venture out into the cold to fill a plastic box with snow.
Add dyes.
Place said plastic box on patio and watch contents melt slowly over the course of three days.
Then, bring box inside and sit it on the back door mat for a further afternoon and evening of melting action:
Eventually get round to emptying the contents into the sink:
Rinse, repeat.
Leave to dry on radiator and admire:
Finally, use snow-dyed fabric to line an impromptu book cover made from teaching sample:
Voila!