Change splash screen for original 7" touch display.
Raspberry Pi Touch Display:
Display size (diagonal): 7 inches
Display format: 800 (RGB) × 480 pixels
Active area: 154.08mm × 85.92mm
I chose the height while maintaining the aspect ratio of 480 px, for the maximum size of the image.
Disable color test/rainbow at start:
the following to the end of the file config.txt "disable_splash=1"
Disable Raspberry logo:
the following to the end of the file config.txt "logo.nologo"
1) Create png image with ideal resolution.
2) copy to /usr/share/plymouth/themes/pix/
3)copy and paste to end of file /boot/cmdline.txt
"quiet splash"
4) save and exit
5) reboot