As we have seen, the characteristics of primary lesions, and sometimes, secondary lesions as well, can be used to create, or narrow, differential diagnoses. This chapter focuses on color as a diagnostic determinant. Color is a powerful tool that can be harnessed to create differential diagnoses. Pink, red, brown, and white are the most common colors of primary and secondary lesions that are manifest in the skin. But the skin may house other colors as well, including yellow, orange, purple, maroon, gray, blue, green, and black. In this chapter, comprehensive differential diagnoses will be discussed for each color using the wheel of diagnosis. Additionally, the causes of generalized color changes will be outlined. While tattoo artists may introduce any of these colors into the skin, this chapter will focus only on those color changes that are endogenously produced or acquired through disease states.
It is important to note that the color of skin lesions is influenced by the color of the skin in which they arise.
The color of skin lesions may be influenced by the background color of the skin they arise in.
The color of normal skin is determined predominantly by the amounts of eumelanin and phaeomelanin that are present, but oxyhemoglobin, deoxyhemoglobin, and carotenoid concentrations also play a role. In darker skin, pink and red colors may be masked, or they may appear purple or brownish. In very light skin, the purple color of lichen planus and other interface dermatitides may not be appreciable, and these papules and plaques may appear pink.
In darker skin, pink and red colors may be masked. In lighter skin, the color purple may appear pink.
The term erythematous is frequently employed to describe lesions in this category. It is useful to differentiate pink from red, and the quality of the red or pink color may connote a specific disease in some instances. Examples include the deep red appearance of infections, such as furuncles and carbuncles, the (sometimes faint) pink color of urticaria (Figure 4.1A), the cherry-red color of cherry angiomas, and the shiny ruby-red color of superficial basal cell cancers. Psoriatic plaques are often described as having a salmon-pink color (Figure 4.1B); cutaneous candidiasis is described as appearing “beefy-red” (Figure 4.1C), and the bright red erythema of an exanthematous drug eruption is known as “drug-red” (Figure 4.1D).
Examples of pink and red dermatoses: (A) Urticaria, showing the classic pink color of wheals; (B) psoriasis, showing a well-demarcated salmon-pink plaque; (C) cutaneous candidiasis with a “beefy-red” appearance and outlying satellite papules; (D) an exanthematous drug eruption displaying a bright red or “drug-red” color.