I use the amber lenses in my Tifosi set for flatter overcast days, or can be used in brightish sunlight in woodland etc.; they lighten things a little, and improve contrast by decreasing glare.
I do a lot of clay shooting, and red lenses (vermillion) are great for lifting the colour of an orange (blaze) clay against a green background, as it flats the green off and increases contrast, but work best on a bright day. Similarly on a duller day (summer, overcast) purple tends to reduce glare, flats off bright green and lifts a coloured clay from the background.