diff --git a/session_4/session_4.Rmd b/session_4/session_4.Rmd
index 84e86ea5eeb336af3667cca5076f6d50c398b28a..9ace90fa1638073e89fa993e983389a5c4e4c114 100644
--- a/session_4/session_4.Rmd
+++ b/session_4/session_4.Rmd
@@ -412,3 +412,26 @@ mutate(
 - Ranking: there are a number of ranking functions, but you should start with `min_rank()`. There is also `row_number()`, `dense_rank()`, `percent_rank()`, `cume_dist()`, `ntile()`
 
 ## See you in [R#5: Pipping and grouping](http://perso.ens-lyon.fr/laurent.modolo/R/session_5/)
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+# To go further:  Data transformation and color sets.
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+There are a number of color palettes available in R, thanks to different packages such as `RColorBrewer`, `Viridis` or `Ghibli`. 
+We will use them here to decorate our graphs, either on data already studied in the training, `mpg`, or on more specialized data such as lists of differentially expressed genes ( GSE86356 )
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+```{r install_colorPal, eval=F}
+install.packages(c("ghibli", "RColorBrewer", "viridis"))
+```
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