General aviation pilot reported a near miss with another aircraft while on the initial approach in the traffic pattern at a non-towered airport. The low wing aircraft pilot did not see the other aircraft; but was notified on the radio; and continued to a safe landing.

Narrative

After local flight I returned to L18; monitored CTAF and reported I was crossing the 15 (about 4 miles out) and entering the 45 to a right downwind for Runway 36. As I Approached the downwind I saw Aircraft Y ahead on the downwind and announced I was entering the downwind to follow the aircraft over the high school. The aircraft ahead called base and turned. I allowed enough space and turned base; announcing I was turning base at the watertank. A few seconds later another Aircraft Z said something like 'well I guess we'll change our plans and that they were also at the water tank.' I continued a normal approach and landing. As I was putting the plane in the hangar the aircraft taxied to their parking spot and I talked to the student who said they did not see me until I called base and they looked off their right and saw me on base. I noticed that the aircraft was colored a dark gray and green or dark blue which probably blended with trees and brush that makes up the hilly background in the area but I saw the other aircraft clearly. As we apparently ended up close together on the downwind; both following the same aircraft. My aircraft is low wing and Aircraft Z is high wing and neither saw the other until I turned base indicating I was probably higher. I have ADS-B in to an Ipad on the panel but it is not wired into the audio system. That would probably have given me an audio alert and my attention was outside entering the downwind and I did not look at the screen. I learned to fly at a non-towered airport over XX years ago and have been based out of non-towered airports for the last YY years but still apparently managed to miss seeing somebody that I should have seen.