my_IplTop_a and mn_SdcardMenu_a control the channels themselves, the tab frame in the background, the "channel" masks, the clock (for the main menu) and the page number label (for the SD menu).
Now, the first entry (property) you come across is ChMask. I can only guess at what this one is, as I haven't actually looked to see a difference when editing it. But considering it uses a blank 16x16 white square, it's probably a lightener for the channels and/or the masks.
The next one you come across is Picture_00. This, along with Picture_01...Picture_04, control the black outline that causes the "TV" look to the channels for the 5 "current view" pages (I say that quoted because in actuality, only one page is fully in view, and two other pages have 3 of their channels in view, except when changing pages).Now, these use only one image file, which is my_IplTopMask4x3, seen right. This is accomplished by the <wrap_s> and <wrap_t> tags. <wrap_s> controls side-to-side wrapping/mirroring, and <wrap_t> controls up and down. By using the value GX_MIRROR, this causes the system menu to display this picture mirrored both horizontally and vertically. This is then mirrored across the entire size of the channel view, making all the channels look like TVs.
The next entries are Picture_05...Picture_09. I don't really know what these do. The utilize the background image my_TVSheet_b, which is a long bar, shaded in the middle, that is repeated. In my themes so far, I haven't really had a use for these, as I use background images that I like to have visible, so I just turn these off (alpha set to zero on all color properties). BaseMask0...BaseMask4 are more that use my_TVSheet_b.
The next one, ChangeTex16x9 I believe serves it's name's purpose. It changes what the channels (Picture00-04) use as their base image from 4x3 to 16x9 in the case of a widescreen view.Now, Edge0...Edge4 use my_IplTopMaskEdge4x3, shown right. This creates the outline on the channels, just inside the outline of the "TVs". It's almost unnoticeable in the menu unless you're really looking for it.
Picture16 does for the Edges what ChangeTex16x9 does for the Masks.
The Line, Shade, and Board entries in the next sets control the "tab" at the bottom of the screen (the border between the background for the channels and the background for the Message Board. If you go into the Board, and move a message down by the clock, you can actually see the message while looking at the channels in the Menu). Line/Shade/Board2 are the "current view" entries.The Line0...Line4 are in charge of the outline for the "tab", shown right. You can see, by mirroring this across the horizon, that you get a tab effect. This is the outline between the board itself and the shadow, or "Shade". Changing the color here is pretty straight-forward.
Shade0...Shade4 control the tab's shadow effect, seen right. Once again, the color change is straight-forward. This is also mirrored once to the right on each page, and not up or down.
The last entries, Board0...Board4, control the color for the tab itself, seen right. Also mirrored to the right on each page.
Then, there are some entries that aren't covered in the style portion of the file, and those are the channel entries themselves. This is because a) if there is a channel there, the style is controlled in its banner information and b) the empy channel animations are controlled by my_IplTop_c for the main menu and mn_SdcardMenu_d for the SD menu. However, the posistions are controlled here. These are the ch_a...ch_e entries. Each entry has sub-entries that are numbered (i.e. ch_b1, ch_b2 ... ch_b12). ch_b, ch_c and ch_d are full twelve-channel sub-entries. C is the current view, b is the one just to the left, and d is the one just to the right. A has three channels, 4, 8, and 12, as that is the one two pages left (only visible just at the end of the transition to a previous page; the channels are then moved to ch_b. Illustrated example to follow). E has channels 1, 5, and 9, and is two pages to the right. You can control the position of them, but I have yet to have success in changing the size on purpose. These entries are simply position holders, or frames, for the channels and the empy animations.
Now, here is the example of the pages. The main part, in full black, is the current view (outlined by green). You can see it includes channels 4, 8, and 12 from b as well as 1, 5, and 9 from d. The red outline to the left shows the view you will see just at the end of a Previous Page transition, which includes the a4, a8, and a12 channel frames. As soon as the animation is completed, the channels in the new "current view" are on the ch_c frames again, and it recenters to the layout below. The same happens the other way, for e1, e5 and e9 (blue outline is Next Page).