Have you looked at the options for ConvexHullMesh in docs? It does have MeshCellHighlight and MeshCellStyle - and you can look up those in docs too and related functions. Please look too at the rest of options I list below and read carefully examples in docs on them, this will help you a lot in future.

ConvexHullMesh[pts, Axes -> True, FrameTicks -> {{-5, 0, 5}, {-5, 0, 5}, {0, 10, 20}}, 
 Boxed -> True, AxesLabel -> {y1, y2, y3}, PlotTheme -> "Scientific", MeshCellStyle -> 
{{2, All} -> Opacity[0.5, Yellow]}, PlotRangePadding -> 1, SphericalRegion -> True]