sips for padding

So I have this applescript... (from this great site http://www.macosxautomation.com/applescript/imageevents/05.html )

set this_file to choose file without invisibles

-- indicate the proportions for the pad area

set H_proportion to 1000

set V_proportion to 1000

try

tell application "Image Events"

-- start the Image Events application

launch

-- open the image file

set this_image to openthis_file

-- get dimensions of the image

copy dimensions of this_image to {W, H}

-- calculate pad dimensions

if H_proportion is greater than V_proportion then

set the new_W to (H * H_proportion) / V_proportion

set pad_dimensions to {new_W, H}

else

set the new_H to (W * V_proportion) / H_proportion

set pad_dimensions to {W, new_H}

end if

-- perform action

padthis_imageto dimensionspad_dimensions--with pad color {65535, 65535, 65535}

-- save the changes

savethis_image with icon

-- purge the open image data

closethis_image

end tell

on error error_message

display dialogerror_message

end try

It works great (kinda!) It will get the current image dimensions and make it square with some padding. The issue? The padding is black. Seems to be a bug in the Image Events app

So I wanna replace this

padthis_imageto dimensionspad_dimensions--with pad color {65535, 65535, 65535}

With something like this

do shell script "sips " & this_file & " -p " & new_H & space & new_W & space & "--padColor FFFFFF" & space & "-i"

So I can get a white background with my image.

I just cant seem to work out the format. Any ideas?

Cheers