I have a 10 unit with blue doors slated to be paid off in 2019.  

I will say that you can find liberal neighbors anywhere you go, but if this is a huge deal for you, you may want to reconsider moving to a more blue area.

You may see an increase in buy demand in some of the lower end blue collar areas.  

Well the fact you said to assume all cash you are pretty much saying that is unlimited since you can compare the same house that in one market would cost $20K and in another might be $2M.Lots of people can buy a $20K for cash not that many can a $2M one.So if you have enough cash to be able to play in most any market then it will usually make sense to work in the blue chip expensive as all hell places since they will retain, and most likely go up the most.  

For future rentals, if they're in blue collar or "average" areas, I wouldn't invest money in sod unless the lawn is completely barren.

We got it for a good price and Thomas tore everything out from the pink & blue carpet, blue laminate counter tops, lavender wallpaper and 1980's appliances to be replaced with stainless steel, granite countertops throughout, new flooring etc.

Watching the ocean waves and the boats come in and out of the dock was one of the few relaxing moments in his day.As he stood there, he watched as a young fisherman headed out and then roughly a half hour later came back with an entire boat full of fish.  

The rents were high as it was by the coast and had an ocean view. 

A nice navy blue with bright white trim and accents would look good in my opinion but then again, as J Scott mentioned, the neighborhood plays a factor.

My DIY yellow letter costs:Yellow Paper $0.02Envelope $0.10Ink $0.02Postage $0.28Total $0.43If I got cheap envelopes I could go even cheaper ($0.35) but I got nice blue invitation envelopes