how to change the top bar backcolor

your color is white
while my color is gray
my code is copy from makensis.nsi
what shall I do more?

!define VER_MINOR 0
!define VER_MAJOR 3

!verbose 3


!include "C:\Program Files\NSIS_2\Examples\WinMessages.nsh"
!include "C:\Program Files\NSIS_2\Examples\Modern UI\ModernUI.nsh"
!verbose 4

!define CURRENTPAGE $9

!define TEMP1 $R0
!define TEMP2 $R1
yours screen shot

my screen shot

my screen shot
it's too ugly

To use the modern UI, you need to include certain macro's, you probably deleted some of them.

Please have a look at the Examples\Modern UI\example.nsi script, that's a better example.