In CATIA V5 when I select a face of a solid only its boundary gets highlighted. Can i highlight the whole face?

By default, only boundary will be highlighted.

To highlight the selected face, Select "Tools > Options > General > Display" on the menu bar and then click on "Highlight faces and edges" and click ok.

To change the highlight color, select "Tools > Options > General > Display > Visualization" on the menu bar and then change the color of "Selected elements".