Format selected row in table

The following is constructive criticism. By design, in Power BI, when you select a

row in a table visual, the selected row is highlighted by default to distinguish it

from other rows.  This is not and never was an indicator of a default row. 

Is your question driven by user feedback for Power BI Reports and Dashboards you support, or

are you expressing a personal opinion and favor for a different default formatting

of the Table and Matrix Visuals?

So, yes, there are ways to impact how row fill is applied, and yes there are ways through 

conditional formatting to make changes.  There are a number of Styles and Theming options,

you can try, though they tend to be set for specific reports and certain templates.   Your question

is interesting, and if you are inclined, you can add a new Idea for a new feature.