Norman - several questions to clarify what you're attempting to do, but you can do pan sharpening in ArcGIS.
First, your subject says ArcGIS 10 - does this mean you are using 10.0?
Second, are you using the image analysis window (IAW) to reference the image, and moving to a Mosaic Dataset (MD) is your alternative, or are you using a MD and just not getting the raster function to work properly? Note with a later version of ArcGIS and a mosaic dataset using the Landsat 8 raster type, pan sharpening may be applied automatically - but for now I'll assume upgrading to a current version is not possible. In 10.0, you can use the IAW to pan sharpen as described in this help topic: ArcGIS Desktop
Note that topic describes exporting to save the image, but you can also simply save the map in MXD format, and any time you need to access the pan sharpened image, reload that MXD. (otherwise, exporting will take up disk space - and with L8, that's a pretty big file!)
If you're using an MD and want to get pan sharpening working in a raster function chain (e.g. you have multiple scenes?), let me know and I can expand on this. This topic may be helpful http://resources.arcgis.com/en/help/main/10.1/index.html#/Exercise_7_Creating_a_pan_sharpened_natura...
...but note it refers to Landsat 7 (implies using the L7 raster type), and I'm guessing it won't work properly with Landsat 8 since the metadata changed - I'd have to work through a test to advise if those instructions would need to be modified for L8...
I'll reply separately re: histogram/color change after clipping.
Cody B.