Those darker stripes or patterns are typically a result of the rolling process during production. Where consistency is critical, pre-finished aluminum or anodized sheets are options for better results, depending on your requirements. Pre-finished sheets come with a factory-applied coating, like paint or laminate, or sometimes alodine/anodizing. They’re ready to use and available in a huge range of colors and gloss/matte finishes. Anodized or alodined aluminum undergoes an electrochemical process that either thickens the natural oxide layer on the surface or adds a chromate layer. Both give a uniform, durable finish while enhancing corrosion resistance. Anodized finishes can also be dyed because they’re porous, but they’re less flexible in terms of texture or pattern compared to pre-finished sheets.