SwatchLegend

Represents swatch-type legend

SwatchLegend[colors_List, labels_List]

where labels can be any Wolfram Expression

Examples

Define firstly

legend = SwatchLegend[{Red, Green, Blue}, {1,2,3}]

and place it to an existing plot

Plot[{x, x^2, x^3}, {x,0,1}, PlotStyle->{Red, Green, Blue}, PlotLegends->legend]

Let it determine colors or expressions automatically

Plot[{Sin[x], Cos[x]}, {x, 0, 5}, PlotLegends -> SwatchLegend["Expressions"]]