1 - Right click the top panel and select "Panel Settings".
2 - Select Apearance tab
3 - Click "solid color (with opacity)
4 - Use Color name: "#0080FF"
5 - Click OK
6 - Click Close.
Unfortunately this method does not store the color. The panel will have a white background after a reboot. To fix this I needed to edit the configuration file.
In a terminal do: gedit ~/.config/lxpanel/LXLE-OSX/panels/panel
Find the line: tintcolor=0
And replace this line with: tintcolor=#0080FF
Save and close gedit
Now write protect (make read only) the panel config file. I did it via the file browser, go to ~/.config/lxpanel/LXLE-OSX/panels, right click panel, properties, permissions, Change content -> Nobody.
Menu->Preferences->Customize Look and Feel -> Select Windows8OS widget theme. -> Apply -> Close
I hope anybody will be able to apply the theme with this guide.
Additional to the above guide, I also minimized the conky system info by commenting out most of the information in the ~/.conkyrc file and changed the font color to black.
I found out that the bug "Unfortunately this method does not store the color. The panel will have a white background after a reboot." is a confirmed bug in LXPanel 0.7.0 and is fixed in 0.7.1. Will this be in the next LXLE release?