Since I can't reproduce the issue with:
I will try later whether it changes anything if I enforce a specific color space for output.
# Imports
import os
import sys
import ctypes
Dllref = ctypes.windll.LoadLibrary("G:/Hybrid/vsfilters/Support/libfftw3f-3.dll")
# Loading Support Fileslsmas
Dllref = ctypes.windll.LoadLibrary("G:/Hybrid/vsfilters/Support/OpenCL.dll")
import vapoursynth as vs
core = vs.get_core()
# Import scripts folder
scriptPath = 'G:/Hybrid/vsscripts'
sys.path.append(os.path.abspath(scriptPath))
# Loading Plugins
core.std.LoadPlugin(path="G:/Hybrid/vsfilters/GrainFilter/AddGrain/AddGrain.dll")
core.std.LoadPlugin(path="G:/Hybrid/vsfilters/DenoiseFilter/FFT3DFilter/vsfft3dfilter.dll")
core.std.LoadPlugin(path="G:/Hybrid/vsfilters/DenoiseFilter/DFTTest/DFTTest.dll")
core.std.LoadPlugin(path="G:/Hybrid/vsfilters/DenoiseFilter/KNLMeansCL/KNLMeansCL.dll")
core.std.LoadPlugin(path="G:/Hybrid/vsfilters/ResizeFilter/NNEDI3/libnnedi3.dll")
core.std.LoadPlugin(path="G:/Hybrid/vsfilters/Support/libmvtools.dll")
core.std.LoadPlugin(path="G:/Hybrid/vsfilters/Support/temporalsoften.dll")
core.std.LoadPlugin(path="G:/Hybrid/vsfilters/Support/scenechange.dll")
core.std.LoadPlugin(path="G:/Hybrid/vsfilters/Support/fmtconv.dll")
core.std.LoadPlugin(path="G:/Hybrid/vsfilters/SourceFilter/LSmashSource/vslsmashsource.dll")
# Import scripts
import havsfunc as havsfunc
# Loading D:\VHS Testing\2017.06.25\source.avi using LWLibavSource
clip = core.lsmas.LWLibavSource(source="C:/Users/Selur/Desktop/source.avi", format="YUV422P8", cache=0)
# making sure input color matrix is set as 470bg
clip = core.resize.Point(clip, matrix_in_s="470bg")
# making sure input color range is set to TV (16-235) scale.
clip = core.std.SetFrameProp(clip=clip, prop="_ColorRange", intval=1)
# setting field order to what QTGMC should assume
clip = core.std.SetFrameProp(clip=clip, prop="_FieldBased", intval=1)
# Deinterlacing using QTGMC
clip = havsfunc.QTGMC(Input=clip, Preset="Slower", TFF=False, InputType=0, TR2=0, Sharpness=1.9, SourceMatch=0, Lossless=0)
clip = core.resize.Point(clip=clip, format=vs.YUV422P8, matrix_s="470bg")
clip = core.std.SetFrameProp(clip=clip, prop="_FieldBased", intval=0)
#clip.set_output()
# resizing to 640x480
resized = core.fmtc.resample(clip=clip, kernel="spline16", w=640, h=480, interlaced=False, interlacedd=False)
resized = core.sub.Subtitle(resized, "Resized")
resized = core.std.AddBorders(resized, 40, 40)
resized = core.resize.Point(clip=resized, format=vs.YUV422P8, matrix_s="470bg")
#resized = core.text.FrameProps(resized)
#clip = core.text.FrameProps(clip)
mixed = core.std.Interleave([clip, resized])
# Output
mixed.set_output()