LaTeX - Add color in equation

In equation environment, we can add color and background color to symbols

• color: \$Y = {\color{red}{5}}x\$ $$Y = {\color{red}{5}}x$$
• background color: \$Y = \colorbox{red}{5}x\$ $$Y = \colorbox{red}{5}x$$

Note: Adding color needs the outermost pair of curly brackets, but adding background color doesn’t need.