ESP32 Forum

In Espressif documentation I've noticed that some times they use 0 (Zero) based numbering and other times it is based on 1 (One):
SD_* is for the signals of the SDIO slave
HS1_* is for the signals of the Port 1 of SDIO host
HS2_* is for the signals of the Port 2 of SDIO host
MT* is for the signals of the JTAG
U0* is for the signals of UART0 module.
U1* is for the signals of UART1 module.
U2* is for the signals of UART2 module.
SPI* is for the signals of SPI01 module.
HSPI* is for the signals of SPI2 module.
VSPI* is for the signals of SPI3 module.
UART is Zero
SPI is One, sometimes

In the same document (ESP32 Chip Pin List) you have an IO_MUX table, the Blue and Red highlighted items are explained but the reason for the green and gray not. I can guess the gray is highlighting that the GPIO20 signal has no pin assigned in the default boot.

More issues:
ESP Technical Reference Table 16: GPIO Matrix Peripheral Signals
What is "Direct I/O in IO_MUX" mean?
I found my answer after a few more hours of reading, the thing that is throwing me is your use of GPIO labels instead of mapping to PIN numbers. I was believing that a PIN could have a different GPIOn mapped since GPIO20 has no pin assigned.

I couldn't find a GPIO list with the pins or GPIO number I could sort so I made one:

Could have saved you some time. I had posted one August 26th - http://esp32.com/viewtopic.php?f=2&t=163&p=884#p884. Not sure if there was any issues with it or updates in the mean time.