The correct answer is:
(a) Red strip on yellow base
Explanation: In Pattern Making for casting, colors are often used to identify different types of components. Loose pieces and seatings typically use the color code of a red strip on a yellow base. This is part of the color-coding system used in the foundry industry to differentiate between different pattern parts, such as core boxes, patterns, and seating parts, making them easily identifiable during assembly and molding.