Use arduino board definitions from http://arduino.esp8266.com/stable/package_esp8266com_index.json - and make sure you're using v2.2.0 or later, this will ensure that pin definitions get set up correctly.

There appear to be two major types of pin layouts for ESP8266 boards. There's a raw layout, where pin 0 is GPIO0, pin 1 is GPIO1, etc... up to pin 16 being GPIO16. Then there's the NodeMCU layout where pin 0 is GPIO 16, pin 1 is GPIO 5, etc...

The library will attempt to, based on board definitions, guess the right layout to use. If it isn't, or if you want to force using a pin to gpio mapping, you can use one of:

#define FASTLED_ESP8266_RAW_PIN_ORDER
#define FASTLED_ESP8266_NODEMCU_PIN_ORDER
#define FASTLED_ESP8266_D1_PIN_ORDER

before you #include <FastLED.h> in your .ino file.

The ESP8266 is a limited platform in some ways. While, on paper, it has 17 GPIO pins, in reality, 6 of these are blocked off from use. GPIO6, GPIO7, GPIO8, GPIO9, GPIO10, and GPIO11 are all unavailable to you. These pins are not defined at all for FASTLED_ESP8266_RAW_PIN_ORDER, and the NodeMCU pin ordering already excludes these 6 pins from its list of available pins.

In addition, if you are using Serial input/output at all, attempting to use GPIO1 for leds will cause the device to reset.

On some boards, if you want to use GPIO15, you may need to follow the instructions here - http://www.instructables.com/id/ESP8266-Using-GPIO0-GPIO2-as-inputs/?ALLSTEPS