In terms of appearance, the HDPE/RH composites with smaller RH particles appeared homogeneous with dark brown color while those with larger particles have a lighter shade of brown as shown in Fig. 7. The fine particle size of 75 μm functioned as a pigment in the HDPE/RH composites. The large RH particle such as at 500 μm, showed up as dark spots on the HDPE matrix. The influence of natural weathering on the visual appearances of the HDPE/RH composites was studied by exposing the HDPE/RH composites specimens to natural UV for 90 days. The exposed HDPE/RH composites were aged as illustrated in Fig. 7. The pure HDPE exhibited light yellow color after the 90 days of exposure. The weathered HDPE/RH composite clearly looked paler in color with greater surface roughness than the non-weathered ones. The corresponded colorations of all the composites in Fig. 7 were measured by L* and a* as clearly listed in Table 1. The appearance of the HDPE/RH composites over the range of the milled RH particle sizes studied appeared differently depending on the RH particle sizes. Before aging, the L* and a* values of the HDPE were 94.67 and 0.02 respectively, they implied that the unfilled HDPE color is white. Regardless of the RH particle sizes, the brown color of the RH was observed uniformly all over the entire surface compared to that of the unfilled HDPE with a decrement in the L* value. This indicated that the composites changed from light to darker shade when the RH was added. The increment in the a* confirmed that the composites were changed from white to the redder shade. Smaller RH particles tend to induce darker color than the larger ones. After natural aging for 90 days, both L* and a*