Thick paint. From the Italian ‘impastare’ - to make paste.
There are two approaches to doing color studies.
Note: In a final painting the traditional approach is not to use thick paint till later on in the alla prima painting process. See thick and thin. However a few artists can get away with using thick paint throughout, although it may not be the best approach. It is okay to do it in these color studies since it is only a study, and the brushwork is not of primary importance in these studies.