Custom label color in QGIS atlas

Question

I'm trying to make an atlas with qgis with a map generating 2 pages (north and south) N and S corresponding to the coverage layer where a field contains the values "N", "S". Every page is formed by the map zoomed on N or S (this is not a problem) and a part where I want the 2 value "N" e "S" changing the font-color: N red and S grey if the atlas zoom the north, N grey and S red if the atlas zoom the south.

I think I can use a conditional expression with label but I'm not able find a way.

To clarify, my problem is the realization of N and S outside the map in the layout with different color:

Answer 1

Since the font color of labels in print composer in QGIS 2.18 can not be data-defined, a workaround is needed. One possible approach is to duplicate the the "N" and "S" labels with black versions on the bottom covered by red versions. The label text can then be written as an expression which only shows the red label if the atlas feature attribute has the corresponding value:

Answer 2

Make a rule based symbology and try this

first rule/filter $id = @atlas_featureid and make your symbolgy

second rule/filter $id <> @atlas_featureid and make your symbolgy