The Collaborative International Dictionary of English v.0.48:

Changeable \Change"a*ble\, a. [Cf. F. changeable.]
   1. Capable of change; subject to alteration; mutable;
      variable; fickle; inconstant; as, a changeable humor.
      [1913 Webster]

   2. Appearing different, as in color, in different lights, or
      under different circumstances; as, changeable silk.

   Syn: Mutable; alterable; variable; inconstant; fitful;
        vacillating; capricious; fickle; unstable; unsteady;
        unsettled; wavering; erratic; giddy; volatile.
        [1913 Webster]

WordNet (r) 3.0 (2006):

changeable
    adj 1: capable of or tending to change in form or quality or
           nature; "a mutable substance"; "the mutable ways of
           fortune"; "mutable weather patterns"; "a mutable foreign
           policy" [syn: mutable, changeable] [ant:
           changeless, immutable]
    2: such that alteration is possible; having a marked tendency to
       change; "changeable behavior"; "changeable moods";
       "changeable prices" [syn: changeable, changeful] [ant:
       unchangeable]
    3: subject to change; "a changeable climate"; "the weather is
       uncertain"; "unsettled weather with rain and hail and
       sunshine coming one right after the other" [syn:
       changeable, uncertain, unsettled]
    4: varying in color when seen in different lights or from
       different angles; "changeable taffeta"; "chatoyant (or shot)
       silk"; "a dragonfly hovered, vibrating and iridescent" [syn:
       changeable, chatoyant, iridescent, shot]

Moby Thesaurus II by Grady Ward, 1.0:

261 Moby Thesaurus words for "changeable":
   able to adapt, adaptable, adjustable, adrift, afloat, agnostic,
   alterable, alterative, altered, alternating, ambiguous,
   ambitendent, ambivalent, amorphous, at loose ends, better, bland,
   brittle, capricious, chancy, changed, changeful, changing,
   checkered, choppy, commutable, commutative, converted, convertible,
   coquettish, corruptible, deciduous, degenerate, desultory,
   deviable, deviant, deviating, deviative, deviatory, dicey,
   different, disorderly, divaricate, divergent, diversified,
   diversiform, dizzy, double-minded, doubting, dubious, dying,
   eccentric, ephemeral, equal, equalizing, equivalent, equivocal,
   erose, erratic, evanescent, even, ever-changing, exchanged,
   faddish, fading, fast and loose, fence-sitting, fence-straddling,
   fickle, fitful, fleeting, flexible, flickering, flighty,
   flirtatious, flitting, fluctuating, fluid, fly-by-night, flying,
   fragile, frail, freakish, fugacious, fugitive, giddy,
   give-and-take, halfhearted, hesitant, hesitating, impermanent,
   impetuous, impressionable, improved, impulsive, incalculable,
   inconsistent, inconstant, indecisive, indemonstrable, infirm,
   infirm of purpose, infirm of will, insipid, insubstantial,
   interchangeable, interchanged, irregular, irresolute, irresolved,
   irresponsible, jagged, jerky, kaleidoscopic, labile, light,
   malleable, many-sided, mazy, mercurial, metamorphic, metamorphosed,
   metastasized, milk-and-water, milky, mobile, modifiable, modified,
   momentary, moody, mortal, motley, movable, mugwumpian, mugwumpish,
   mushy, mutable, mutant, mutual, neutral, nonconformist, nondurable,
   nonpermanent, nonstandard, nonuniform, of two minds, passing,
   perishable, permutable, plastic, pliant, pluralistic, polysemous,
   protean, proteiform, qualified, quicksilver, ragged, rambling,
   rebuilt, reciprocal, reciprocating, reciprocative, reformed,
   renewed, resilient, restless, retaliatory, returnable, revived,
   revolutionary, rough, roving, rubbery, scatterbrained, shapeless,
   shifting, shifty, short-lived, shuffling, skeptical, skittish,
   spasmodic, spineless, sporadic, standard, subversive, supple,
   swapped, switched, tasteless, temporal, temporary, touch-and-go,
   toying, traded, transformable, transformed, transient, transitive,
   transitory, translated, transmuted, transposed, unaccountable,
   uncertain, unconfirmable, uncontrolled, unconvinced, undecided,
   undependable, undetermined, undisciplined, undivinable, undurable,
   unenduring, unequable, unequal, uneven, unfixed, unforeseeable,
   unmitigated, unorthodox, unpersuaded, unpredictable, unprovable,
   unreliable, unresolved, unrestrained, unsettled, unstable,
   unstable as water, unstaid, unsteadfast, unsteady, unsure,
   unsystematic, ununiform, unverifiable, vacillating, vagrant, vapid,
   variable, variegated, variform, various, varying, versatile,
   vicissitudinary, vicissitudinous, volatile, wandering, wanton,
   watery, wavering, wavery, wavy, wayward, whimsical, wishy-washy,
   worse