There are several screen color options in Source Insight, and options that control appearance.
To quickly change the visual theme, select Options > Visual Theme and choose a theme. You can also change and define new themes. See: Visual Themes.
To change screen colors for the main application window and various display elements, use the Options > Preferences: Color command. See: Color Options.
Each panel window has its own font and color settings. Edit the settings and select the desired fonts and colors in all panels. A quick way to set them all at once is to use the Options > Preferences: Color & Fonts tab and click the Set Panel Fonts and Colors button.
Source Insight has many display options for formatting source code.
To fine-tune options about how syntax elements are formatted in general, select Options > Preferences: Syntax Formatting, and Options > Preferences: Syntax Decorations.
To change the appearance of syntax elements, such as how delimiters are styled, or how declarations appear, select Options > Style Properties. This controls the colors, fonts, font sizes, and other styling applied to these elements. See: Style Properties.