A warm filter is a photographic filter that improves the color of all skin tones and absorbs blue cast often caused by electronic flash or outdoor shade.
[1] They add warmth to pale, washed-out flesh tones and are ideal for portraits as they smooth facial details while adding warmth to skin tones (for color imaging).
[2] In general, they suppress blue casts on overcast days and on subjects lit by blue sky.
[3]