A process and associated system for creating color effects in extrudable material, such as plastic and metal for example, are presented. Flows of first and second viscous materials of respective colors are provided and then combined in a predetermined pattern to form a stream of combined viscous material. In a first aspect, the flow rate of the first viscous material is caused to vary over time in order to vary an amount of the first viscous material in the stream. In a second aspect, which may be used alone or in combination with the first aspect, the first and second viscous materials have distinct viscosities to reduce an amount of color blending between the first color and the second color in the stream of combined viscous material. A static mixer may then be used to apply a predetermined dividing, overturning and combining motion to the stream of combined viscous material to partially mix the first viscous material and the second viscous material, such that upon exiting the static mixer, the first material of the first color and the second material of the second color form a color pattern in the stream of combined viscous material. Sheets of extrudable material may be created using such process and used in the manufacturing of many different products including for example kayaks and stand-up paddle boards.