Since you are using Graphviz to do the drawing you need to use the attributes that Graphviz understands. See http://www.graphviz.org/content/attrs

import networkx as nx
G = nx.Graph()

G.add_node(1,color='red',style='filled',fillcolor='blue',shape='square')
G.add_node(2,color='blue',style='filled')
G.add_edge(1,2,color='green')
G.node[2]['shape']='circle'
G.node[2]['fillcolor']='red'

A = nx.to_agraph(G)
A.layout()
A.draw('color.png')
print A.to_string()

Gives

strict graph {
    graph [bb="0,0,107.21,46.639"];
    node [label="\N"];
    1    [color=red,
        fillcolor=blue,
        height=0.5,
        pos="18,28.639",
        shape=square,
        style=filled,
        width=0.5];
    2    [color=blue,
        fillcolor=red,
        height=0.5,
        pos="89.21,18",
        shape=circle,
        style=filled,
        width=0.5];
    1 -- 2   [color=green,
        pos="36.338,25.899 47.053,24.298 60.519,22.286 71.18,20.694"];
}