If you need 15 different colors (one for each client), you will need vba to
do it.  If you only need 2 colors (empty, not-empty), then use conditional
formatting - it requires no vba)

If you need many colors you could do something like this:
'assumes data rows start at 3 and client column is A

LastRow = Cells(Rows.Count, 1).End(xlUp).Row
for i = 3 to LastRow
   DO CASE
       CASE Cells(i,1).value = "Client 1"
           cells(i,1).select
           With Selection.Font
               .Name = "Arial"
               .FontStyle = "Bold"
               .Size = 10
               .Strikethrough = False
               .Superscript = False
               .Subscript = False
               .OutlineFont = False
               .Shadow = False
               .Underline = xlUnderlineStyleNone
               .ColorIndex = 5
           End With
       CASE Cells(i,1).value = "Client 2"
               Same code, different values
       CASE Cells(i,1).value = "Client 3"
           etc

       End Case
next i

Hope this helps

Glen

Hard to give any detailed answer without knowing more.  The main question is
how you decide which shelf(cell) to use when you have a new delivery.  Also,
how do you plan on assigning colors for new clients - would this be a random
choice?

My approach would be:
1) Have a list of your clients on a separate worksheet tab along with any
other info needed, and also use a cell in this list set to the proper color
that you can use both as a color key to your warehouse map and as a cell that
can be copied/paste format in order to apply that client's color to the cells
in the map.
2) Build a userform for entering deliveries/pick ups.  You could use a
combobox linked to your client list for selection of the client (along with
an "add new" option).
3) Once the userform is filled in, use a command button to run code that
applies whatever logic you use to decide which shelf/cell gets filled (or
emptied).  If filled, copy the color-formatted cell from your client list and
paste it in the map to create the proper color.  If removed, reset the cell
to the default format, e.g. MapCell.Interior.ColorIndex = xlColorIndexNone.

This just sketches out an approach to doing what you describe; the
individual elements (list format, userform, combobox, etc) you can find other
examples in this newsgroup that would help you put them together.  The only
part that would be particular to your need is the logic behind the code that
determines how to find the proper cell in your map; only you  know how you
are doing this and without understanding your procedure I can't tell you how
to write code that would do it for you.