(*  shrinking Rectangles, not rotated, with changing colour  *)
c = {Black, Red, Blue, Green, Magenta, Cyan, Yellow};
g = Table({{t/2, t/2}, {6-t/2, 6-t/2}}, {t, 0, 5});
h = ReplaceAll(g, {{x1_, y1_}, {x2_, y2_}} -> {{x1, y1}, {x2, y1}, {x2, y2}, {x1, y2}, {x1, y1}});
Graphics({Riffle(c,
   Table(Line(Flatten(Part(h, k), 0) ) ,{k, 1, Length(g)}) )
  }, PlotRange -> {{-3,7}, {-1,9}}  (*  {L, R}, {B, T}  *)
)


(* single Rectangles, rotated around {0,0} by Pi/4 (45 degrees), with changing colour  *)
c = {Black, Red, Blue, Green, Magenta, Cyan, Yellow};
g = {{-3, 0}, {3, 6}};  (*  diagonal of rectangle  *)
h = Replace(g, {{x1_, y1_}, {x2_, y2_}} -> {{x1, y1}, {x2, y1}, {x2, y2}, {x1, y2}, {x1, y1}});
g = {};
Do(
    x = Part(h, t, 1);
    y = Part(h, t, 2);
    r = Sqrt(x^2+y^2);
    a = ArcCos(x/r);
    g = Append(g, {N(Cos(a+\[Pi]/4)*r), N(Sin(a+\[Pi]/4)*r)});
  , {t, Length(h)});
gPlot = Append({h}, g);  (*  original box & modified box  *)
Graphics({Part(c, 3), Line(Part(gPlot, 1)),
    Part(c, 2), Line(Part(gPlot, 2))
 }, PlotRange -> {{-7,4}, {-3,7}}  (*  {L, R}, {B, T}  *)
)


(*  shrinking Rectangles, rotated around {3,3} by Pi/12 (15 degrees), with changing colour  *)
c = {Black, Red, Blue, Green, Magenta, Cyan, Yellow};
gPlot = {};
For(t = 0, t < 6, t++,
    h = {{t/2, t/2}, {6-t/2, t/2}, {6-t/2, 6-t/2}, {t/2, 6-t/2}};
    h = Append(h, Part(h, 1));
    A = {{N(Cos(t*\[Pi]/12)), N(Sin(t*\[Pi]/12))}, {N(-Sin(t*\[Pi]/12)), N(Cos(t*\[Pi]/12))}};
    R = h - 3;
    g = R.A + 3;
    gPlot = Join(gPlot, {g})
);
Graphics({Riffle(c,
   Table(Line(Part(gPlot, k)) ,{k, 1, Length(gPlot)}) )
 }, PlotRange -> {{-3,7}, {-1,9}}  (*  {L, R}, {B, T}  *)
)