Just disable it. It has nothing to do with power issues, it is just a boot logo. You can at the same time disable smooth OpenGL scaling. If you want blocky pixels, it will interfere. If you disable smooth scaling, you will see the rainbow image is just 4 pixels, like the Windows Logo in 4 colours.
sudo nano /boot/config.txt
comment:
# dtparam=audio=on
add:
disable_splash=1
disable_audio_dither=1
scaling_kernel=8
sudo nano /boot/cmdline.txt
dwc_otg.lpm_enable=0 console=ttyAMA0,115200 console=tty3 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline fsck.repair=yes rootwait quiet loglevel=3 consoleblank=0 vt.global_cursor_default=0 logo.nologo
sudo nano /etc/modules
comment out both snd-bcm2835 to #snd-bcm2835
sudo nano /lib/modprobe.d/aliases.conf
comment out to prevent conflict getting sound device index number
# options snd-usb-audio index=-2
The other stuff deals with the USB audio interface (you will need that too, see other topic!)