I try the following codes:
import torch
from torch import nn

# Set (RGB)*2 = (0, 100, 200), (300, 400, 500)
x = (torch.arange(6, dtype=torch.double)*100).view(1, -1, 1, 1)

conv = nn.Conv2d(in_channels=6,
                 out_channels=2,
                 kernel_size=1,
                 stride=1,
                 padding=0,
                 groups=2,
                 bias=False)

# Set Conv weight to 1
conv.weight.data = torch.ones(6, dtype=torch.double).view(2, 3, 1, 1)

output = conv(x)

print(output)

output = (500, 5000). The result seems to be your Guess 2, RR GG BB.