Sailor top is not a base game item, you probably have sby's loader bundle with the mod called "moreclothing" that adds a lot of other mods
The "moreclothing" files are located in \sby_loader_pack_12_545d\Loader5.45\Mods\$INIT$\moreclothingmods\
Those are all Adobe Flash .swf files. They are not easily editable. You would have to use software like JPEXS to rip or decompile the assets.
You will then get vector art images called .svg files
You can edit those in any vector art app, however. To remake them back into game assets you will need proprietary Adobe software like FlashCS6 or CCAnimate. There are tutorials on this forum on how to use the modding templates to create sdt mod .swf files. Spceciflly you will need the RGB import tutorial.
If this is daunting you can instead make a revision request here on the forum to turn the mod into an RBG version capable of being color edited using the default games menus though which is not always done originally because doing so requires a lot more work. Please include links or some how directly reference which mod you'd like a revision of.
Welcome to the SDT modding community, we hope you brought your computer science degree :D