Static Texture is better, you can find good one in engine:
/Engine/EngineSky/VolumetricClouds/T_CloudPattern.T_CloudPattern
How mat works:
you get perlin noise texture (or make one in photoshop/gimp).
then you get single b/w chanell
stretch its UV coordinates, until whole material displays only single pixel or so
then you pan it and rotate (or just one of those is sufficient but both make better randomness)
For timers, stretching etc use PRIME numbers it gives less probability for creating repeatable loops
Finaly you feed that random stretching and rotation as ALPHA into linear interpolate
and interpolate between two colors, they can be same just different brightness
EDIT: (for more advanced pplz):
make green blue and yellow codes into single material function.
then copy that perlin texture into 3 parameter nodes (with same node name)
now connect them all to 3 different copies of that function
and MULTIPLY RGB result pins from texture then clamp it 0..1
and feed that as ALPHA. This will make really nice random blinking.
But its overkill imo. 