WHY DID WINDOWS 7, FOR A FEW MONTHS, LOG ON SLOWER IF YOU HAVE A SOLID COLOR BACKGROUND?

Summary from the TLDR Web Dev newsletter

Windows 7 briefly experienced slower logons when using a solid color background. The issue was from the system's design, which waited for all desktop components to report their readiness before dismissing the Welcome screen. When a solid color was used, the wallpaper readiness signal was never sent, causing a 30-second delay.