The mail piece I use is a hand written yellow letter stuffed in an unsealed envelope.

No one knows its a yellow letter until they open it, so consider the envelope as importantly as the content you write. 

It's a harder decision when they are pink or yellow, but in my opinion, the blue looks pretty nice.

I find houses that look unkempt in otherwise nice neighborhoods and I mail out a yellow letter.

Secondly, I'm trying to avoid marketing to these motivated sellers as a "hoity toity" real estate investment firm called "Capitol Wealth Builders" when I'm trying to buy their property for steep discounts, and felt "SellHomeNowDMV" could just be a domain I own and do business as when marketing to these folks (postcards, craigslist, yellow letters, etc.). 

I knew I could do better than this, I am driven and I don't need a warm hand to guide me along the yellow path. lol Shortly after this I bought Tim Bell's Wholesale Flight Plan, this is a very short easy read that is highly recommended.

I know we have someone here that specializes in sending out yellow letters but I can't remember his name.  

Landlording can be a unique challenge sometimes (like 6 inches of snow in one day this week; or last year a large bear tossed a full dumpster into a ditch (hint -- just tow it out with a yellow tow strap, 4 x4 as a ramp and pull with a truck or jeep). 

Mad props for the vivid use of vocabulary!

Sending a single postcard or yellow letter would be pretty expensive but possible sure.