The size of the sheet tabs and font on them are governed by the setting for
Scrollbars in Windows Display Appearance. Mine are at 18. Start there and
work your way up or down.
So: with Excel Application closed.
Win98 as example...
Start > Settings > Control Panel > Display > Appearance
"Item" drop down select Scrollbars
Change setting to Taste
Apply
OK
Depending upon your settings, you may have to re-boot to see the changes.
Also note: this is a Global change and will affect all Applications.
As far as colored tabs go, you must have Excel 2002 or later. Right-click on
a tab and "Tab Color".
Gord Dibben Excel MVP