Now i know the way.
The fellowing method is appealed to davedontmind’s post (https://forums.eagle.ru/topic/96291-how-to-edit-the-controls-indicator-window-ctrlreturn in 6th level)
Here take the Ka-50’s controls indicator for example, we could change the size, location and color by edit the ControlsIndicator_page.lua (*:\SteamLibrary\steamapps\common\DCSWorld\Mods\aircraft\Ka-50\Cockpit\Scripts\ControlsIndicator\ControlsIndicator_page.lua)
1. Size & locatgion
Default size: local size = 0.15
Default location: base.init_pos = {0,-(1 - 1.5*size)}
You could edit the number to custom the size and location(yes, you have to try until you find your most suitable)
2. Color
Background color
local orange_mat = MakeMaterial("",{0,200,0,50})
The numbers in {0,200,0,50})represent red, green, blue and Alpha, range 0-255. Alpha value 0 meas total transparent.
Line color
Add
local line_mat = MakeMaterial("arcade.tga",{255,100,0,125})
below the
local orange_mat = MakeMaterial("",{255,100,0,0})
Change
pitch_scale.material = "ARCADE_3_RED"
to
pitch_scale.material = line_mat
Change
roll_scale.material = "ARCADE_3_RED"
to
roll_scale.material = line_mat
Indicator sign color
Change
stick_position.material = "ARCADE_3_RED"
to
stick_position.material = "ARCADE_RED"
Add
rudder_index.material = "ARCADE_RED"
below the
rudder_index.parent_element = rudder_scale.name
Add
collective_index.material = "ARCADE_RED"
below the
collective_index.parent_element = collective_scale.name
Add
tick.material = "ARCADE_RED"
below the
tick.controllers = {{"throttle",i,rud_sz}}
Others
txt_brakes.material = "font_ARCADE_RED" [easy to know it’s the color of the brakes txt]
wheel_brake_mask.material = "GREEN_TRANSPARENT" [wheel_brake sign mask]
wheel_brake.material = "RED" [wheel_brake sign]
txt_autopilot.material = "font_ARCADE_RED" [easy to know it’s the color of the autopilot txt]
txt_autopilot_hover.material = "font_ARCADE_RED" [the color of the hover txt]
The "ARCADE_RED","RED","GREEN_TRANSPARENT" are in the materials.lua(*:\SteamLibrary\steamapps\common\DCSWorld\Mods\aircraft\Ka-50\Cockpit\Scripts\materials.lua)
here is the final effect