Atlético de Madrid plays in red and white stripes with blue shorts, which is why it is called “Rojiblancos.” The nickname “Colchoneros” (mattress makers) is usually traced to the stripes looking like the mattress fabric of the time. Blue appears on the shorts and the crest. The HEX codes are common approximations, not official club values.
These are commonly used reference values; they can vary by source, material or screen.