Hi Gavin,
Your posted picture looks like a summer shot. Assuming your current fall scene has the same 3 white trees as your summer shot, you can find the object library and object information on the matching 3 trees shown in my fall scene (although green) that are placed by my HC_Clem_Tillion_Trees_PLC_BA_rtmm_fall.bgl file below:
<P3D root Directory>\Scenery\Global\scenery\vegetation_fsxrtm.bgl:
veg_ccedarincense2_old1 {e2762d82-389e-4333-93e8-8e24b4a4e961} (FSX only!)
veg_ccedarincense3_old3 {75426beb-e6c0-4e39-8fa9-83b88f8fe947} (FSX only!)
veg_ccedarincense3_old5 {c87702f7-22e9-4cd2-87bf-e9307022e3a3} (FSX only!)
These 3 objects show up green in my fall scene at Halibut Cove but apparently show up frosted white in yours. It is possible that the default object library vegetation_fsxrtm.bgl referenced above might be corrupt or using a corrupt default texture on your system. All 3 objects above use the same default treesconifer.dds file (it is a texture sheet) which is found in the associated <P3D root Directory>\Scenery\Global\texture folder.
Rod