Is it safe providing scan copy of sale deed to unknown ?

Please be assured that your client will not be able to misuse it even though the color scanned copy looks like Original. 

Gone are the days when people could misuse producing coloured Xerox too fool Banks or financial institutions. Now the Banks/ Financial institutions follow a very stringent Due Diligence and frauds / misuses have reduced considerably. 

But just check the credibility of the buyer who is asking for a scanned copy.

why do you need a color copy ?

give a black and white and SCRIBLLE as COPY on top of it  , make it clearly visible -

Dear Sir

This is the best suggestion. 

Thank you for your suggestion. 

I will write "COPY" on top of all papers and then send it to the client.