Difference between arduino wifi modules

What is the difference between arduino wifi module ESP 01 and 8266? First one is black and second one is blue otherwise they look same

These are not Arduino boards, but they are compatible with the Arduino IDE. The ESP 01 is the same as the ESP8266-01 by a slightly different name. The main difference between older and newer ESP8266 boards is the amount of RAM. The blue boards generally had 512K where the black boards (generally, there is no "standard", will have either 1mb or 4mb. Some of the newer boards have an LED on GPIO1, mapped by the IDE as ledBuiltIn.

Now, if you are thinking of using an ESP8266 as a WiFi board for the Uno, I can't help you. If I need WiFi, I use a board that already has WiFi. Not some bizzare mating of an ESP to an Uno.

SteveMann:
Now, if you are thinking of using an ESP8266 as a WiFi board for the Uno, I can’t help you. If I need WiFi, I use a board that already has WiFi. Not some bizzare mating of an ESP to an Uno.

Which board is it? Any suggestions?

Depends on what you want to do with the board.
A "WeMos D1 mini" or "NodeMCU" are small and cheap, with more than enough WiFi capabilities than you might ever need.
But they have limited I/O and 3.3volt logic, which might or might not be a problem.
Leo..

another141:
Which board is it? Any suggestions?

There are several ESP based boards. I personally prefer the Wemos D1 Mini. If I need more I/O, I use the NodeMCU.
We might be able to help more if we knew what the project was.