If you are on Home Premium, Enterprise, Professional or Ultimate then you can change it from "Personalize>Windows Color"
Just right click on the desktop and go to Personalize and there you would see "Windows Color" Second option in the bottom.
And if you wish to change it in the theme itself try @ "Taskbar & SystemTray > TaskBand > Aero > TaskBand > Background Bottom "
This sometimes happens in you have other toolbars added on the taskbar. Right click the taskbar/toolbars and uncheck any that are active and try again. I have the same thing on mine but mine is intentional, I like the way mine looks with central taskbar icons.
Is it a custom theme or are you just changing it in personalization
Danny
My Computer
At a glance
Windows 7 Home Premium x64 SP1intel(R)core(TM)2 duo CPU T6600 @ 2.20GHz3 gb ddr3ati radeon hd4570/512mb
Welcome to the Seven Forums
As Danny asked are you using a 3rd party custom theme?
If so it may have been built wrong, try changing the way Taskbar buttons are displayed. Right click on taskbar go to Properties In the Taskbar tab use the dropdown arrow and change it and Apply and see if it changes.
Jerry
My Computer
At a glance
Win 7 Pro x64 / Win 10 ProIntel(R) Core(TM) i7-3630QM CPU @ 2.40GHz12 GB(1) Intel(R) HD Graphics 4000 (2) NVIDIA GeFo...
Computer type
Laptop
Computer Manufacturer/Model Number
Sager NP9170
OS
Win 7 Pro x64 / Win 10 Pro
CPU
Intel(R) Core(TM) i7-3630QM CPU @ 2.40GHz
Motherboard
CLEVO P170EM
Memory
12 GB
Graphics Card(s)
(1) Intel(R) HD Graphics 4000 (2) NVIDIA GeForce GTX 675M
Sound Card
(1) Realtek High Definition Audio (2) Intel(R) Display Aud
Monitor(s) Displays
17.3
Screen Resolution
1920x1080
Hard Drives
(1) Samsung 860 EVO 500GB(OS) (1) Samsung 860 EVO 500GB(Data)
Keyboard
Backlite
Antivirus
MSE, Malwarebytes Pro
Browser
Firefox
Other Info
DESKTOP: Custom-built.
OS: Win 10 Pro x64.
CASE: Rosewill R5.
CPU: Intel I5 4670K CPU @ 3.40GHz.
CPU COOLER: Cool Master Hyper 212 EVO.
MOTHERBOARD: Asus Z87-A.
MEMORY: Kingston HyperX 2x4 GB.
GPU: Nvidia Geforce 650 TI.
PSU: Corsair TX750.
DRIVES: (1) Samsung 840 120 GB SSD (2) Western Digital blue 500 GB 7200 RPM.