Blue outside and red inside classic color scheme

Quick answer：

This refers to a classic color scheme where the exterior of an object or space is blue and the interior is red. It is often used for aesthetic or functional reasons. For instance, in architecture or design, this color scheme can create a striking contrast and visual appeal. In technology, blue and red are sometimes used to indicate different states or functions, such as 'on' and 'off' or 'hot' and 'cold'.