I had this problem recently when my grey/white cat turned into a grey/ginger cat! He had rubbed himslef in a pile of builders sand and had orange feet, face, chest and neck, even his grey bits had a ginger tinge! I got a towel and dampened it with warm water and tried to rub it off him but he wasn't happy about me doing it so I gave up.
I think as Oscar is blind and new to you it might be a bit worrying for him being rubbed down. Sheilas ideas of squeezing a bit of warm water on his paws sounds I good idea as this will encourage him to do the washing himself!
With his eyes you can clean them gently with cooled boiled water on cotton wool, a separate ball for each eye to minimise the chances of spreading if there's any infection.