Revision | Flash | Power LED | Blue LED
--------------|-------|-----------|-------------
Blue ESP-01 | 512k | None | TX/GPIO1/low
Black ESP-01 | 1M | Red | TX/GPIO1/low
Black ESP-01S | 1M | Red | IO2/low
OTOH I think one will need to use an ESP12 for serious business anyway (and it has 4 MB flash).