\textcolor{ red} \mathrm\boldsymbol{rm \; bold \; ABC \; def}  \  \;  \ \mathit\boldsymbol{italic \; bold \; ABC \; def} \; \ \textcolor{Blue} \math {normal \; ABC \; def}  \; \ \textcolor{Blue} \mathcal {cal \; ABC \; def} \;  \ \mathbb{bb \; ABCdef     

\textcolor{ red} \mathrm\boldsymbol{rm \; bold \; ABC \; def}  \  
\;  \ \mathit\boldsymbol{italic \; bold \; ABC \; def} 
\; \ \textcolor{Blue} \math {normal \; ABC \; def}  
\  \mathcal{cal \; ABCdef}   \;  \ \mathbb{bb \; ABCdef   

Serif

Sans-Serif