Is Listsource just providing a list of homeowners and then you need to add a label to your postcard?

Does Listsource just providing a list of homeowners and then you need to add a label to your postcard?

EXAMPLEI have a deal in riverside where I did an off market purchase from one of my marketing postcards for 210K and the ARV is probably 310K at least.

I already got my targeted list from list source and now need to make sure my postcard is ready as well.

What is a good size for the post card and should it be in color?

@Patrick Philip, trying different types of postcards, mailers, whatever, to see which is more effective amongst a given mailing list.  

Thank you all for your answers I am marketing more on Facebook and I have seen some leads come in, I was to keep marketing that way and eventually target a zip code and mail out postcards or some type of value that brings is the numbers

Have you found better success with handwritten letters, postcards, handwritten envelopes but printed letters, a mix of multiple alternating?

I do simple yellow postcards sent to absentee owners...so far so good.My printer does everything except the list...simple and quick.Happy to share his contact info and pricing if interested.

I'm inclined to think that postcards / yellow letters may get brushed aside, so something that looks like a bill or an official notice may do the trick, possibly with a more formal message inside?