如何更改 Latex Beamer 中的颜色主题（针对整个演示文稿）？

Question

我需要为每一帧添加蓝色和白色的背景。

\documentclass[11pt]{beamer}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{graphicx}
\usepackage{ragged2e}
\usepackage{etoolbox}
\usepackage{setspace}
\usepackage{lipsum}
\usepackage{pdflscape}
\usepackage{amsmath,amsthm,amsfonts,mathrsfs,amssymb}
\usepackage{amssymb,latexsym,pstricks,pst-grad}
\usepackage{enumerate}
\usepackage{array}
\usepackage{multirow}
\usepackage{rotating}
\usepackage{longtable}
\usepackage{pdflscape}
\usepackage[english]{babel}
\usepackage{booktabs}
\usepackage{tabularx}
\usepackage{colortbl}
\usepackage{array, makecell}
\usepackage{siunitx}
\usepackage{caption}
\usepackage{float}
\usepackage{graphicx}
\usepackage{mathtools}
\usepackage{fontenc}
\usepackage{multicol}
\apptocmd{\frame}{}{\justifying}{} % Allow optional arguments after frame.

\usetheme{focus}
\fontfamily{times new roman}
\begin{document}
    \begin{frame}
        content..This is my first beamer
    \end{frame}
    \end{document}