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Crushed-rock layers have been widely used in roadway embankments in warm permafrost regions to preserve the permafrost ground via the convective cooling through the cavity of the rock layer. Under the scenario of global warming, reducing the solar absorption of the rock layer for further preserving the permafrost in the roadbed has gained momentum recently. Except the convective cooling, the albedo, temperature, and heat flux of a rock layer are also fundamentally correlated to the thermal performance of the layer but have not been fully understood. Here we prepared three crushed limestone layers with mean particle sizes of 15.0, 24.4, and 36.5 mm, respectively. We sequentially coated rock surface with different colors. After a rock layer was coated to be unicolor by a matte paint, we measured the layer's albedo and logged the heat flux and temperature at the bottom of the layer simultaneously. The measurement lasted for two days; then the layer was coated by another paint to have a different color and the next measurement cycle started. We found that a smaller-particle crushed-rock layer absorbs less sunlight, stays cooler, transmits less heat downward, and has smaller thermal inertia. It is also found that a smaller-particle rock layer has a lower probability to trap the reflected radiation on the rock surface. Special efforts should be made to lowering this probability for curtailing the absorption of solar radiation by crushed-rock layers to embankments.