\documentclass{article}
\usepackage{threeparttable}
\usepackage{multirow}
\usepackage{booktabs}
\usepackage{xcolor}
\usepackage{tikz}
\begin{document}
\begin{table}[!ht]
\setlength\tabcolsep{0pt}
\centering
\begin{threeparttable}
\begin{tabular}{@{\extracolsep{2ex}}*{2}{cc}}
\toprule
\textcolor[RGB]{255,0,0}{Red} and \textcolor[RGB]{0,0,255}{Blue}\tnote{\textbf{\textcolor[RGB]{255,170,0}{Orange}}} & \textbf{\textit{\underline{\textcolor[RGB]{0,204,0}{Green, bold, italic, underlined}}}} \\
\textcolor[RGB]{0,0,255}{\textcolor[RGB]{255,0,0}{Nested red }and blue} & \textcolor[RGB]{171,205,239}{0.985} \\
\bottomrule
\end{tabular}
\begin{tablenotes}[flushleft]
\footnotesize
\item[\textbf{\textcolor[RGB]{255,170,0}{Orange}}]This annotation should have \textit{italics}
\item[]This footnote should have \textbf{bold}
\end{tablenotes}
\end{threeparttable}
\end{table}
\end{document}