The dark blue-green to deep green, leathery leaves of Protea lacticolor grow crowded and overlapping near stem-tips, the blades curving upwards, while some merely ascend. The short-stalked to nearly stalkless blades are lanceolate to ovate, even elliptic. The bases are heart-shaped to tapering, and the tips broadly tapering.
The lower parts of the midribs in picture are red on the upper surfaces like the stems, whitish on the lower surfaces. Higher up on the blades the midribs lose colour and disappear from sight near the tips. Lateral, ascending veins are mostly hard to see. Softly hairy when young, the leaves are hairless and nearly smooth when mature.
The leaf dimensions are 7 cm to 11 cm long by 2,5 cm to 5 cm wide (Coates Palgrave, 2002; Rebelo, 1995; Bond and Goldblatt, 1984; Rourke, 1980; iNaturalist).