I chose the exact color by first looking on-line at doors with house exteriors that were similar to mine. Then went to the paint store (Home Depot for me) and took several paper color samples that might be a consideration. Then I taped those sample papers to the door and left them there for about a week. Viewing them as I came and left the house at different times of the day.
I found just the right color and confirming with my husband, for his opinion was important too. Now it was time to clean and dry the front of the door. I sanded the front of the door, scraped edges of inside window with a straight blade. Took brown outdoor caulking and caulked the outer glass window frame. Let that dry for 24 hours. Then taped all around the inside of the window and door handles and hardware with tan paper like tape (I think masking tape is the name). I waited for a warm dry day and a day I could be home for 8-12 hours. Put down painters plastic under the door and on top of my wood floor. I had bought paint with primer in a small can. I got a satin and not gloss. Those were the choices. I asked the guy how much I needed for a door and he gave me a little can and it was plenty. It was pricey, but I wanted this door painted.
I had a paint brush that was about 4 inches wide and a very small water color paint brush for touch ups later. I painted one coat with my son. He insisted on helping. He used one of his kids thick water color paint brushes. The first coat was messy, but having my son help priceless. I told him thank you and I let that coat dry until dry to the touch. That took about 3 hours. Then I painted the second coat. Yes, even with a primer I had to do a second coat. This is usually the case for any color I have had to painting over. Though I have noticed primer helps with painting over dark colors in general. The paint brushes washed out with warm soapy water very easy. I washed out the brushes and layed them out to dry each time I finshed a coat. My brush was not perfectly dry for the second coat, but close and it worked well.
The door felt dry about 4 hours later. Not a complete dry, but enough to take off the tape. (you could use the blue painters tape it is very similar and probably stronger). Now I took my very small paint brush and did tough up around areas where the tape had been.
Finally evening came and I shut the door. I love the color with the black trim. Now I need to motivate painting the trim a better black coat. It is old and coming off. There is also sap seeping out of the wood too. I bet chalk paint was used on the trim too. I will have to get some nicer paint on that at some point.
I noticed today that there is a scratch on the door and it scraped the paint off to the black. Ug. That is what I get for painting a steel door and well this was not a professional paint job. It was a mommy has a day at home and the door is not coming off the hinges type of job. Will have to paint over that again. The worst part is that after I painted and the first freeze came, I noticed the window fogging on the inside. Just in one corner. It is an older home. I am just going to have to live with it for now because I like my green door.