<｜begin▁of▁sentence｜>### Instruction:
Suppose you have a simple undirected graph G with 3 nodes and 2 edges, and you want to render this graph to a PNG file with a light background, with nodes positioned at predefined coordinates. All nodes should have the same color. How can you use the `save_graph` function from `graspologic.layouts` to generate this visualization and save it to a file?
### Response:
import networkx as nx
from graspologic.layouts import NodePosition, save_graph

# Create a simple graph using NetworkX
G = nx.Graph()
G.add_nodes_from([1, 2, 3])
G.add_edge(1, 2)
G.add_edge(2, 3)

# Define the positions for each node
positions = [NodePosition(node_id=1, x=0.0, y=0.0),
             NodePosition(node_id=2, x=1.0, y=1.0),
             NodePosition(node_id=3, x=2.0, y=0.0)]

# Define the node colors
default_color = '#1f78b4'  # A blue color
node_colors = {node: default_color for node in G.nodes}

# Render the graph to a .png file
output_path = 'my_graph.png'
save_graph(output_path=output_path, graph=G, positions=positions,
          node_colors=node_colors, light_background=True)
<|EOT|>
