Añadida explicación sobre añadir color al ggheatmap.

vignettes/citfuns.Rmd

@@ -88,6 +88,11 @@ By default, *other variables not used are eliminated* during the grouping proces
 ggheatmap(df, exclude_group = "Met")+facet_grid(.~Met, scales = "free")
 ```
 
+You can specify a color instead of being transparent to the tiles:
+```{r,  fig.width=8}
+ggheatmap(df, color="black")
+```
+
 Finally, you can scale the heatmap either by rows or by columns:
 
 ```{r, fig.width=8}