I am just a fellow player
There is an in-game helper, where on a subject of signal flares the following is written:
"Communication of target designation can be signaled with white and blue flares at night and black smoke at day, each commander and vehicle crew has a limited number of these signal flares. N.B. This type of communication is inaccurate and unreliable.
Red flares are used by the enemy to signal the end of an attack. White & green flares signal the start of an attack or movement. Magenta is used by forward air observers for signaling targets to air support."