why rainbowduino got opposite negative and positive ?

I am using the "Rainbowduino LED driver platform - ATmega328" see as http://www.seeedstudio.com/wiki/Rainbowduino_LED_driver_platform_-_ATmega328 and I have decided to using a digital meter to check the voltage and it got me confused by the output the current from rainbowduino. It supposed positive number but i got a negative number. Why? If I want to change the digital meter to positive I would have to change from red clip to the blue wire of rainbowduino ( see letter red on rainbowduino which is negative number) . The image see the below. http://imgur.com/nCFiuY8

Actually, I am using the Funduino v1.0 not same as the other such as rainbowdunio, colordunio. Please help me thanks!

Where is the image?



p.s. the brown wire is TX are attched to Arduino UNO.

For voltages connect the black (COMM) lead to ground.

For current in, connect the red (+ve) lead to the +ve supply, black lead to the load (which would normally be connected to the +ve supply.